Tyrosinase (EC 1.14.18.1) is a key enzyme in pigment biosynthesis of organisms. trans-Cinnamaldehyde thiosemicarbazone, a derivative of benzaldehyde thiosemicarbazone, was synthesized as an inhibitor of tyrosinase. The inhibitory effects of this compound on the activity of mushroom tyrosinase were investigated. The results showed that trans-cinnamaldehyde thiosemicarbazone could potently inhibit both monophenolase activity and diphenolase activity of tyrosinase. For monophenolase activity, trans-cinnamaldehyde thiosemicarbazone could not only lengthen the lag time but also decrease the steady-state rate. For diphenolase activity, the IC(50) value was determined to be 5.72 microM. Kinetic analyses showed that trans-cinnamaldehyde thiosemicarbazone was a reversible and mixed type inhibitor on this enzyme. The inhibition constants (K(I) and K(IS)) were determined to be 4.45 and 8.85 muM, respectively. Furthermore, the antibacterial activity against Bacillus subtilis, Escherichia coli, Staphyloccocus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia, and Agrobacterium tumefaciens was investigated. The results showed that trans-cinnamaldehyde thiosemicarbazone was more effective against B. subtilis and S. aureus with the same minimum inhibitory concentration (MIC) of 50 microg/mL and with the same minimum bactericidal concentration (MBC) of 50 microg/mL.