This research work is based on the synthesis of derivatives of tetrazole and benzimidazole and screening of their biological activities. Spectroscopic techniques, i.e. 1H-, 13C-NMR, EI-MS, HREI-MS, and IR spectroscopy were used to determine the structures of the synthetic compounds. This dissertation consists of three chapters depending on the different libraries of synthetic compounds. The biological evaluation of the compounds is given in summarized form. Each chapter has its own compound, table, figure, and schemes number. Chapter-1: This chapter consists of two parts. First part is about syntheses of 5-phenyl-1H-tetrazole derivatives by a newly developed methodology and their screening which resulted in identifying some lead molecules for further studies. We have synthesized twenty-six derivatives through this methodology and among twenty-six, three compounds are new. Library of synthetic compounds showed potent α-glucosidase inhibitory potential, four compounds exhibited remarkable inhibitory activity superior to standard acarbose. These tetrazoles may act as lead compounds in search of more potent α-glucosidase inhibitors. The synthetic compounds were screened for their β-glucuronidase inhibitory activity as well, three compounds showed moderate activity. These compounds were screened for their phosphodiesterase inhibitory activity too, two compounds showed excellent inhibitory activity more active than standard. Compounds were also showed good xanthene oxidase inhibitory activities as six compounds showed moderate to good activity. Compounds were tested for their antyglycation potential also, Four compounds found to be active than standard. In antileishmanial studies three compounds showed moderate to good inhibition. Moreover, this library was screened for β-cell viability assay and nine compounds showed good to moderate results. The second part of this chapter consists of twenty-nine compounds. Among the whole series, twenty-four are new and five compounds are known. Compounds have been synthesized using water as solvent using cost effective and commercially available starting materials. Synthetic compounds showed potent antiglycation activity, fourteen exhibited good inhibitory activity compareable to standard. These compounds were tested for their immunomodulatory activity too, seven compounds showed good to moderate activity showing there IC50 values close to standard. In antileishmanial potential, three showed moderate to weak activity. In β-cell viability assay only three compounds showed very weak activity. Chapter-2: We have optimized a nucleophilic aromatic substitution reaction to synthesize tetrazolyl ethers by using cesium fluoride as a suitable base. The higher cost of cesium fluoride is offset by clear advantages such as higher yields, short reaction time, and small amount of reagents required and easy work-up. Thirteen compounds are new among the whole series. Evaluation of biological activities of twenty-four compounds based on tetrazole skeleton resulted in identifying some lead molecules for future studies. Compounds were evaluated for their antleishmanial activity and four compounds showed moderate antileishmanial activities. Chapter-3: This chapter consists of three series of 1H-benzimidazole which have been synthesized using DMSO as a solvent and commercially available starting material. In first series, thirteen compounds are new; these synthetic compounds showed excellent potential in antiinflammatory assay, five exhibited potent antiinflammatory activity. These compounds were also screened for their antidiabetic activity, five compounds showed very good activity. Compounds of this library were tested for their urease inhibitory activity too and two showed weak inhibition. In addition, compounds were screened for their antileishmanial activity and sixteen compounds showed good to significant activity. Other two series of benzimidazole derivatives were also synthesized and seven compounds are new while the rest are known, these are screened for leishmanicidal and glycation activity and exciting results results were found.