The synthesis of some new heterodiazole and their annulated imidazo[2,1-b]1,3,4-oxa/thiadiazolone 6a-d, 7a-d; 1,3,4-oxa or thiadiazole[3,2-a]pyrimidine diamine 8a-d and 1,3,4-oxa or thiadiazole-3-piperidino-1-propamide 11a,b derivatives have been described. The obtained compounds were evaluated for their in-vitro antitumor activity. A single dose (10 μM) of the test compounds were used in the full National Cancer Institute (NCI) 60 cell lines panel assay. Compounds 6c and 6d displayed appreciable anticancer activity against leukemia, non-small cell lung, CNS and showed moderate activity against colon, melanoma, and breast cancer cells lines. Compound 6c possessed remarkable broad-spectrum antitumor activity which almost 4 fold more active than the known drug 5-FU with GI(50), TGI, and LC(50) values of 6.0, 17.4, and 55.1 μM, respectively.