The inhibitory effects of a series of 5,6-dihydro-4H-1,3-selenazine derivatives, 1,3-selenazole, and 5,6-dihydro-4H-1,3-thiazine derivatives on the proliferation of human HT-1080 fibrosarcoma cells were investigated. The compounds 4-ethyl-4-hydroxy-2-p-tolyl-5, 6-dihydro-4H-1,3-selenazine (TS-2) and 4-hydroxy-4-methyl-6-propyl-2-p-tolyl-5,6-dihydro-4H-1,3-selenazine++ + (TS-6) exhibited the strongest inhibitory effect among 1, 3-selenazine derivatives, and the EC(50) of TS-2 and TS-6 was 7.76 and 8.40 microM, respectively. On the other hand, 1,3-selenazole and 5,6-dihydro-4H-1,3-thiazines had no inhibitory effects. TS-2 and TS-6 inhibited the proliferation of HT-1080 cells time- and dose-dependently. They induced dose-dependent DNA fragmentation in HT-1080 cells, revealing a typical apoptosis characteristics. The present study demonstrated that TS-2 and TS-6 inhibited HT-1080 proliferation through the induction of DNA fragmentation.