This thesis describes the synthesis, characterization and bioassay of some novel five and six membered heterocyles and biheterocycles. Some new 2-(3,5-dimethoxy-4-methylphenyl)-4-aryl-1,3,4-oxadiazoles (1a-h) were synthesized by microwave irradiation of 3,4-dimethyoxy-4-methylhydrazide (6’) with substituted benzoic acids in the presence of thionyl chloride. Compound (1b) exhibited significant bacterial inhibition while compounds (1a), (1e) and (1f) showed significant antifungal activities. Except for compounds (1e), (1f) and (1h), the rest were active for their phytotoxic activities. Some N-aminomethyl substituted aryl-5-aryl-1,3,4-oxadiazole-2-thiones (2a-j) were synthesized. Reaction of substituted hydrazides (1’-8’) with ethanolic solution of carbon disulfide and potassium hydroxide afforded 1,3,4-oxadiazole-2-thiones as key intermediates, which were refluxed with substituted anilines and paraformaldehyde in ethanol to undergo mannich condensation to furnish N-aminomethyl substituted aryl-5- aryl-1,3,4-oxadiazole-2-thiones (2a-j). Compounds (2b) and (2g) displayed maximum bacterial inhibition whilst (2b) showed maximum antifungal activity. All compounds were phytotoxic except the compound (2h). 5-Aryl-1,2,4-triazole-3-thiones (3a-f) were synthesized by reaction of substituted hydrazides (1’-8’) with ethanolic solution of carbon disulfide and potassium hydroxide. Compound (3d) and (3e) showed maximum antibacterial activity. In case of antifungal activities compounds (3b) and (3f) were most active. Except compounds (3b) and (3f) all other were active for their phytotoxic activities. The triazoles (3a-f) were converted into corresponding 3-aryl-6-phenyl-1,2,4- triazolo-[3,4-b][1,3,4]-thiadiazines (8a-f) by the condensation with 2-bromo acetophenone. Compound (8a) and (8e) showed maximum antibacterial and antifungal inhibition respectively. All compounds except (8d) and (8e) showed positive phytotoxic activity. The substituted hydrazides (1’-8’) were also microwave irradiated with acetyl acetone to afford 3,5-dimethylpyrazoles (4a-h). Compound (4b) was most active antibacterial whilst (4a) and (4d) were most active antifungal agents. All compounds were phytotoxic except (4a), (4f) and (4h). i 1-Aroyl-3,5-diarylpyrazolines (5a-h) were synthesized by cyclization of substituted hydrazides (1’-8’) with suitably substituted chalcones (a-b). Compounds (5a) and (5c) showed maximum inhibition in case of antibacterial activities and maximum percentage inhibition in case of antifungal activities. All pyrazolines were active for their phytotoxic activities. Microwave accelerated oxa-Pictet Spengler reaction of 2-chlorophenyl ethanol with various aryl aldehydes afforded some 1-aryl-5-chloroisochromans (6a-j). Standard homologation sequence of the 2-cholobenzoic acid afforded the 2-chlorophenylacetic acid which was on esterification and reduction with sodium borohydride in tetrahydrofuran and methanol furnished the 2-chlorophenylethanol. The latter was irradiated with substituted benzaldehydes in the presence of p-TsOH acid to afford 1- aryl-5-chloroisochromans (6a-j). Isochroman (6c) showed maximum inhibition against B. subtilis whereas (6e) showed against maximum inhibition E. coli. Isochromans (6a) and (6d) were most active as antifungal agents. All compounds were active for their phytotoxic activities except (6a), (6d) and (6g). Some N-substituted morpholines (7f-j) were also prepared. Thus α-amino alcohol were protected with para-tolyl methyl sulfinate in the presence of n-butyl lithium to get N-substituted sulafanilamides (7a-e), which were cyclized with bromoethyl diphenyl sulponium triflate in the presence of sodium hydride to get N-substituted morpholines (7f-j). Deprotection of the substituted morpholines was carried out by stirring with 2 N hydrochloric acid to get morpholinium salts (7k-m). 3,4,5-Trimethoxybenzoic acid was converted into corresponding phenylacetic acid. The latter upon esterification followed by reduction with sodium borohydride in tetrahydrofuran and methanol afforded the 3,4,5-trimethoxyphenylethanol. Cyclo- condensation of phenylethanol with methyl acetoacetate in the presence of p-TsOH gave methyl isochromanyl esters (a-c) which were treated with hydrazine monohydrate to furnish the corresponding hydrazides. Condensation of the latter with acetyl acetone afforded isochromanyl pyrazoles (9a-c). Compound (9a) was most against both strains of bacteria; compounds (9b) and (9c) were most against in case of antifungal activities. All compounds were active for their phytotoxic activities except (9a), and (9c). Trimethoxyisochromanyl hydrazide (c) was treated with various substituted phenyl isothiocyanates to obtain the corresponding thiosemicarbazides (10a-e). Acid catalyzed intramolecular cyclization of thiosemicarbazides afforded the isochromanyl thiadiazoles (11a-e) whist base catalyzed intramolecular cyclization furnished the corresponding isochromanyl triazoles (12a-e). In this series compounds (11c) and (12d) showed maximum inhibition against both strains of bacteria while maximum antifungal inhibition was showed by compounds (11b) and (12c). All compounds were phytotoxic. The structures of all of the synthesized compounds were confirmed by IR, HNMR, 13CNMR and Mass analysis.