The inhibitory effects on tyrosinase of the methanolic extracts from 10 Nostoc strains were investigated. The results show that the inhibitory action for the above 6 strains of Nostoc enhanced with the increase of concentration of the methanolic extracts. The methanolic extracts of Nostoc sp. FACHB892 has great inhibitory capacity on tyrosinase, of which the inhibitory rate is 60.54% at concentration of 33.3 mu g/mL, while the methanolic extracts of other 5 strains ( Nostoc sp. FACHB95, Nostoc sp. FACHB106, N. punctiforme FACH13252, N. calcicola FACHB389 and N. parmiloides FACHB392) exhibitted weaker inhibitory effects. The inhibitory rates are 41.55% 37.58% 46.94% 52.12% and 47.95% respectively at the same concentration. The inhibitory mechanism of the methanolic extracts of Nostoc sp. FACHB892 on tyrosinase is reversible and noncompetitive indicated by the enzymatic kinetic analysis.