This dissertation deals with phytochemical and bioactivities studies on indigenous medicinal plants; Maytenus royleanus (Celastraceae) (Part A), Ficus faveolata (Moraceae) (Part B) and additional miscellaneous part C (Cyclotetrapeptides from Aspergillus ochraceopetaliformis). Part-A Part A deals with phytochemical and bioactivities studies on the chemical constituents of the roots of Maytenus royleanus. The systematic phytochemical studies have led to the isolation and structure elucidation of three new compounds (1-3). In addition seven known compounds (4-10) have also been isolated for the first time from this species. Structures have been elucidation by advanced spectroscopic techniques. Royleanine A (1) 1β,2β,5β,7β,8β,11-Hexaacetoxy-4-hydroxy-3α,15-[2'',3''-dimethyl-3''(5''''-carboxy- 2''''-pyridyl)-propanoic acid] dicarbolactone-dihydro-agarofuran Royleanine B (2) 1β,2β,5β,7β,8β,11-Hexaacetoxy-3α,15-[2''-methyl-4''(5''''-carboxy-2''''- pyridyl)-butanoic acid] dicarbolactone-dihydroagarofuran Royleanine C (3) 1β,2β,5β,7β,8β,11-Hexaacetoxy-3α,15-[2''-methyl-2''β-benzoate-4''(4''''- carboxy-2''''-pyridyl)-butanoic acid] dicarbolactone-dihydroagarofuran Salaspermic acid (4) Orthosphenic acid (5) 3α,22β-Dihydroxyolean-12-en-29-oic acid (6) Oleuropein (7) Ligutroside (8) Quercetin (9) β-Sitosterol-3-O-β-D-glycopyrannoside (10) Part-B Part B deals with isolation and characterization of chemical constituents from Ficus faveolata. Five compounds were isolated from the stem methanolic extract of Ficus faveolata; two of them are new (11, 12) and three known compounds (13-15) hitherto unreported from this source. Their structures have been elucidated by spectroscopic techniques. Ficusonic acid (11) 3β,21β-Dihydroxy-olean-12-en-29-oic acid Ficusonolide (12) 3α-Hydroxylean-12-en-29,19α-olide Gallocatechine (13) β-Sitosterol-3-O-β-D-glycopyrannoside (14) 3β,22β-Dihydroxyolean-12-en-29-oic acid(15) Part-C Part C is the miscellaneous section which describes the isolation and characterization of two new Cyclotetrapeptides; ochrine A (16) and ochrine B (17) from the fungal strain Aspergillus ochraceopetaliformis collected from Hawaii shallow water sediment. Their structures have been elucidated by modern spectroscopic techniques.