A number of hydrazide derivatives of the non-protein amino acid L-canavanine (Cav) and its structural analogue Lnorcanavanine (NCav), have been synthesized and their growth-inhibitory effects evaluated in cultured non-tumor 3T3 cells and tumor cell line HepG2 by the MTT assay. The Cav derivatives (Cav-CONHNC6H5, Cav- CONHN(CH2CH2Cl)2, and Cav-CONHNH2) and NCav derivatives (NCav-CONHNHC6H5 and NCav- CONHN(CH2CH2Cl)2 exhibited higher cell growth inhibitory effects on both cell lines compared to their parent compound. These effects were considerably higher on the tumor cells HepG2 in comparison to the non-tumor 3T3 cells. Introduction of the hydrazide group constitutes an effective structural modification, which significantly amplifies the growth inhibitory properties of the parent compound against tumor cells HepG2. These results confirm our previous conclusion that a proper hydrazide modification of the carboxylic group of Cav and its analogues may lead to a significant increase in the inhibitory effect of the compounds on the growth of tumor cells. On the other hand, NCav derivatives showed higher cytotoxicity on the HepG2 cells in comparison with the respective canavanine analogues. Evidently the length of the carbon side chain influences the cytotoxicity of the compounds also.