A series of novel methylthio-, sulfinyl-, and sulfonyl-8H-thieno[2,3-b]pyrrolizin-8-oximino derivatives 7A-12P was designed and synthesized as anti-tumor agents. Their structures were confirmed by IR, (1)H-NMR, MS, and elemental analysis. The anti-tumor activities of all the target compounds were tested by the MTT method in vitro against Bel-7402 (human liver cancer) and HT-1080 (human fibro sarcoma) cell lines. Among them, compound 11N (IC(50) = 18.2 microM, 8.2 microM), was the most promising compound of all synthesized molecules, it was 2.5- and 3.3-times more active than cisplatin (IC(50) = 45.2 microM, 26.7 microM), respectively.