Two Keggin-type polyoxometalates (POMs) containing glycine, (HGly)(3)PW12O40 and (HGly)(4)SiW12O40, were synthesized and evaluated as mushroom tyrosinase inhibitors. The spectrophotometric method results showed that both (HGly)(3)PW12O40 and (HGly)(4)SiW12O40 could strongly inhibit the diphenolase activity of the tyrosinase and that their inhibition mechanisms were reversible. Their half-inhibition concentration values were estimated to be 1.55 and 1.39mmol/L, respectively. The inhibition kinetics analysis by Lineweaver-Burk plots indicated that (HGly)(3)PW12O40 was an uncompetitive inhibitor with K-IS=0.046mmol/L, whereas (HGly)(4)SiW12O40 was a noncompetitive inhibitor with K-I=K-IS=2.17mmol/L. This study may help to extend the application of POMs in the fields of medicine and food preservation. (C) 2015 International Union of Biochemistry and Molecular Biology, Inc.