The research work included in the present dissertation is mainly focused on isolation and structure elucidation of pure chemical constituents from the selected high altitude plants belong to Ligularia, Senecio and Vernonia genera. Moreover, biological activities have also been incorporated for various crude fractions and the purified compounds. There are three main parts of the dissertation: Part-A: Phytochemistry and bioactivities of Ligularia thomsonii Part-B: Phytochemistry and bioactivities of Senecio desfontainei and Senecio chrysanthemoides Part-C: Phytochemistry and bioactivities of Vernonia anthelmintica Part-A Part A describes the phytochemical investigation and bioactivities of L. thomsonii (Compositae). Three new (32-34) along with nine known (35-43) compounds were isolated from the plant. Various spectroscopic techniques were used to characterize their structures. Compounds (32-36 and 39-43) were also evaluated for their radical scavenging activities in the diphenylpicrylhydrazyl (DPPH) assay using ascorbic acid as standard. Part-B Part B deals with the phytochemistry and bioactivities of S. desfontainei and S. chrysanthemoides (Compositae). One new (44) and eleven known compounds (45-55) were isolated from S. desfontainei while six known compounds (56-61) obtained from S. chrysanthemoides. Physical characteristics and extensive spectroscopic studies were used for characterization of the isolated and purified compounds which were also evaluated for their antioxidant activities. Part-C Part C of the dissertation, describing the phytochemistry and bioactivities of V. anthelmintica (Compositae). Eleven new compounds (62-72) were isolated and their structures have been characterized by physical characteristics and advanced spectroscopic techniques.