4-Dimethylaminobenzaldehyde-thiosemicarbazone (DABT) and 4-dimethylaminobenzaldehyde-N-phenyl-thiosemicarbazone (DABPT) were synthesized and established by H-1 and C-13 NMR and mass spectrum. Both compounds were evaluated for their inhibition activities on mushroom tyrosinase and their anti-tyrosinase kinetics was investigated. The results showed that both compounds exhibited significant inhibitory effects on activity of monophenolase and diphenolase; DABT and DABPT decreased the steady-state rate with 1.54 mu M and 1.78 mu M as their IC50 values respectively. The inhibitory effects of diphenolase activity exhibited sharp in a dose-dependent manner and their IC50 values were estimated as 2.01 mu M and 0.80 mu M, respectively. Kinetic analysis showed that their inhibition mechanism was reversible. The inhibition type of DABT was mix-type with inhibition constants K-I = 1.77 mu M and K-IS = 6.49 mu M, while that of DABPT displays non-competitive with the inhibition constant K-I = 0.77 mu M. (c) 2012, The Society for Biotechnology, Japan. All rights reserved.