In the present study 18 novel imidazole-(benz)azole and imidazole-piperazine derivatives were synthesized in order to investigate their probable anticancer activity. The structures of the compounds were confirmed by IR, H-1 NMR and EI-MS spectral data. Cytotoxicity (MTT), analysis of DNA synthesis and detection of apoptotic DNA assays were applied to determine anticancer activity of the compounds against colon (HT-29) and breast (MCF-7) carcinoma cell lines. Most of the compounds, showed greater activity against HT-29 cells than MCF-7 cells. Some of them indicated considerable cytotoxicity against both of the carcinogenic cell lines. However, their inhibitory activity on DNA synthesis was relatively poor. Anticancer activity screening results revealed that 11, 12 and 13 were the most active compounds in the series. They exhibited significant cytotoxicity against both of the carcinogenic cell lines and caused DNA fragmentation of the HT-29 cells. (C) 2010 Elsevier Masson SAS. All rights reserved.