Thiazolylpyrazoline derivatives were recently reported as potent anticancer agents. In this study, novel 1,4-phenylene-bis-N-thiocarbamoylpyrazoles (3a-h and 1,4-phenylene-bis-pyrazolylthiazoles (5a-h were prepared and screened for their anticancer activities against C6 (rat brain tumor cells) and HeLa (human uterus carcinoma). Anticancer activity studies were performed as a dose-dependent assay starting with eight concentrations. 5-Fluorouracil (5-FU) was used as a positive control. Compounds 3c, 3d, and 3h were examined and they revealed almost the same activities compared with 5-FU in terms of cell selectivity against C6 cells. Moreover, compounds 3a-h had lower cytotoxicity than 5-FU. The low cytotoxicity values of 3a-h as well as their high antiproliferative activity were encouraging, but further studies are required on the use of these molecules as anticancer drugs.