Twenty pseudo-peptide thioureas IIa-l containing α-aminophosphonate moiety were synthesized from the reaction of chiral α-amino carboxamide derivatives Ia-c with O,O'-dialkylisothiocyanato(phenyl)methylphosphonate 5. The synthesized compounds were completely characterized by elemental analysis, physical and spectral (IR, (1)H NMR, (13)C NMR) data. According to the preliminary studies on antitumor activities, compounds IIa-l could inhibit tumor cells PC3, Bcap37 and BGC823. These compounds displayed low to high activity by MTT assays. Among them, L-IIk, D-IIa and D-IIe were identified as potent inhibitors, with IC(50) values ranging from 4.7 to 11.2 μM according to in vitro assay.