This dissertation describes the essential oil analysis, antioxidant, antimicrobial and allelopathy of two plants belonging to the genus Teucrium and Perovskia namely, Teucrium royleanum Wall. ex Benth., and Perovskia atriplicifolia Benth. belonging to the family Lamiaceae. The Teucrium royleanum was also subjected to the isolation and characterization of the secondary metabolites. Investigation of T. royleanum resulted in isolation of three (3) new compounds, the skeletons of two belonging to terpenes, named as royleanumin 1, and royleanumioside 2, while the third was named as royleanumoate 3. The compounds 1 and 2 were subjected to allelopathy assays against lettuce seedlings (weed). Compound 1 exhibited remarkable phytotoxic activities and could prove as a lead compound for the development of environmentally friendly weedicides. The known compounds isolated from this plant included, 5-hydroxy-4,7-dimethoxy flavone 4, 5,7-dihydroxy-3,4-dimethoxyflavone 5,4′, 6-dihydroxy 5,7-dimethoxyflavone 6,3,4-dihydroxymethylbenzoate 7, oleanolic acid 8, β-sitosterol 9 and β-sitosterol glucoside 10. The literature survey reveals that flavonoids are good allelochemicals and thus the characterized 5-hydroxy-4,7-dimethoxyflavone 4, 5,7-dihydroxy-3,4-dimethoxyflavone 5, 4′,6-dihydroxy 5,7-dimethoxyflavone 6 were subjected to the allelopathy assays. All compounds exhibited strong allelopathy activities to the test lettuce seedlings. Consequently, these compounds can also be used as lead structures for studies on the development of new synthetic herbicides. iiAnalysis of the essential oil obtained from Teucrium royleanum Wall. ex Benth. by means of GC-MS resulted in qualitative and quantitative identification of forty six known compounds comprising of sesquiterpene hydrocarbons (42.2 %), oxygenated sesquiterpenes (21 %), monoterpene hydrocarbons (17.3 %), oxygenated monoterpenes (7.7 %). The antioxidant capacity of the essential oil was evaluated by means of 1, 1-Diphenyl-2-Picryl-Hydrazyl (DPPH) and superoxide anion methods. The same essential oil was also subjected to allelopathy assays and showed promising results. Teucrium royleanum was tested by four variant assays in a separate set of experiments using lettuce seeds, showing excellent inhibition of the growth of lettuce seedlings. The plants leaf leachates were assayed by Sandwich and Homogenated Sandwich methods while Dish Pack Method was used for the evaluation of essential oils. The above stated methods confirmed the presence of allelochemicals in T. royleanum and were further evaluated in bioassay guided way by total activity approach. The crude methanolic extract fractionated with n-hexane, chloroform, ethylacetate, butanol and water fractions were assayed by the Total Activity Method. The essential oils, n-hexane and chloroform fractions played a significant role in our findings. The results from this study suggested that the secondary metabolites from Teucrium royleanum can be potential candidates for the phytotoxicity (Allelopathy). Analysis of the essential oil obtained from Perovskia atriplicifolia Benth. by means of GC-MS resulted in the qualitative and quantitative identification of eighteen compounds. The major constituents were camphor (28.91%), limonene (16.72%), ά-globulol (10.21%), trans-caryophyllene (9.30%), and ά-humulene (9.25%). Antimicrobial activity of the oil was evaluated using Agar Diffusion Method and Agar Dilution Method. The antimicrobial test results showed that the oil possesses significant antimicrobial activity iiiagainst ten bacteria. The bacterial strains tested were Bacillus cereus, Bacillus cerus subsp. mycoides, Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus faecium, Escherichia coli, Enterobacter aerogenes, Pseudomonas aeruginosa, Klebsiella pneumoniae (clinical isolate), and Yersinia enterocolitica respectively and five fungal strains namely Candida albicans, Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Aspergillus parasiticus, and Geotricum candidum (wild type). The over all results of our studies on the essential oil of P. atriplacifolia suggests it to be a good source of antimutagenic and antimicrobial agents and thus can prove as a good candidate for utilization in the cosmetics, food and pharmaceutical industries.