The steady-state kinetics of catalytic action of Penicillium vitale catalase has been studied. The enzyme reaction conforms to the Michaelis-Menten equation, which is shown by considering the initial velocity of the enzyme-catalytic reaction with increased concentrations of hydrogen-peroxide and sodium perborate. The parameter Km value is rather large (231-259) mM. On the other hand the Pen, vitale catalase is one of the more active enzymes and shows kcat values equal to 0.8-3.0 x 10(-6) s-1 and kcat/Km ratio of the order of 0.4-1.2 x 10(7) M-1 s-1. The enzyme reaction conforms to the Arrhenius equation when the temperature varied from 0 to 60 degrees C. It shows a slight temperature dependence and extremely low Ea value: 1.48 kcal/mol.