This thesis is prefaced by a brief literature review covering the biological activity of imidazole and fused imidazole derivatives. In addition, a brief literature survey covering the general methods used for the synthesis of imidazole and fused imidazole derivatives were given. A critical discussion and detailed survey for the experimental results attained with an adequate interpretation is advanced. Imidazole and its derivatives gained remarkable importance due to their widespread biological activities and their use in synthetic chemistry. Accordingly, in this investigation, it was of interest to synthesize some novel imidazole and fused imidazole derivatives. The sequence of reactions followed in the preparation of the designed compounds is summarized in the following schemes: Scheme 1 deals with the preparation of 5-arylidine-3-phenyl-2-thioxoimidazolidin-4-ones (2a-c) starting from 3-phenyl-2-thioxoimidazolidin-4-one (1) via stirring compound 1 with different aldehyde in ethanol containing piperdine. Alkylation of compounds 2a-c using methyl iodide gave the thioethers 3a-c. Aminolysis of 3a-c with different primary and secondary amines afforded compounds 4a-h. On the other hand, hydrazinolysis of the thioethers 3a-c using hydrazine hydrate gave the key intermediates 5a-c. Scheme 2 describes the Condensation of the 2-hydrazino derivatives 5a-c with different aromatic aldehydes which afforded the hydrazone derivatives 6a-j. Also, the novel compounds 7a-c and 8a-c were obtained through the reaction of compounds 5a-c with isatin and 4-methyl benzene sulfonyl chloride respectively. Scheme 3 comprises the cyclization of 2-hydrazino derivatives 5a-c using acid chloride, ethyl chloroformate, nitrous acid to afford the corresponding products 10a,b, 12a-c and 13a-c. Scheme 4 involves the synthesis of imidazotriazine derivatives 14a-c, 15a-c and 16a-n via cyclization of compounds 5a-c with pyruvic acid, chloroacetyl chloride and phenacyl bromide derivatives respectively. The structure elucidation of new compounds was supported by elemental analysis, IR, 1HNMR, 13CNMR, in addition to mass spectroscopy. Some of the newly synthesized compounds were evaluated for their cytotoxic activity against breast carcinoma and colon carcinoma cell lines. The cytotoxic activity showed that compound 5c was the most active one against breast carcinoma (IC50=3.3 ug/ml) and colon carcinoma cell (IC50=4.73 ug/ml) lines. Antimicrobial screening of some of the newly prepared compounds showed that most of the tested compounds exhibited high activity against gram positive Staphylococcus aureus (ATCC 6538), Staphylococcus epidermidis (ATCC 12228) and micrococcus spp. (ATCC 10240), gram negative Klebsiella pneumonia (ATCC 27736), Salmonella typhimurium (ATCC 14028), and Escherichia coli (ATCC 10536) ) bacterial strains and Aspragillus niger (ATCC 16404) and Candida albicans (ATCC 10231) fungal strains.