Here a new class of hydroxy- or methoxy-substituted 5-benzylidene(thio)barbiturates were designed, synthesized and their inhibitory effects on the diphenolase activity of mushroom tyrosinase were evaluated. The results showed that several compounds had more potent tyrosinase inhibitory activities than the widely used tyrosinase inhibitor kojic acid (IC50=18.25μM). In particular, 3',4'-dihydroxylated 1e was found to be the most potent inhibitor with IC50 value of 1.52μM. The inhibition mechanism analysis revealed that the potential compounds 1e and 2e exhibited such inhibitory effects on tyrosinase by acting as the irreversible inhibitors. Structure-activity relationships' (SARs) analysis also suggested that further development of such compounds might be of interest.