Catalase is the major H 2 O 2 -scavenging enzyme in all aerobic organisms. From the cDNA sequences of three rice (Oryza sativa L.) genes that encode for predicted catalases (OsCatA, OsCatB, and OsCatC), complete ORFs were subcloned into pET21a and expressed as (His) 6 -tagged proteins in Escherichia coli. The recombinant (His) 6 -polypeptides were enriched to apparent homogeneity and characterized. With H 2 O 2 as substrate, the highest catalase k cat value (20 AE 1:71 Â 10 À3 min À1 ) was found in recombinant OsCatB. The optimum temperatures for catalase activity were 30 C for OsCatA and OsCatC and 25 C for OsCatB, while the pH optima were 8.0, 7.5, and 7.0 for OsCatA, OsCatB, and OsCatC respectively. All the catalases were inhibited by sodium azide, -mercaptoethanol, and potassium cyanide, but only weakly by 3-amino-1,2,4-triazole. The various catalases exhibited different catalase activities in the presence of different salts at different concentrations, OsCatC showing higher salt inhibitory effects than the two other OsCats.