Aldolase with a specific activity of 10.8 units/mg protein was isolated from pig muscle. Its molecular weight was found to be 150,000. The optimum pH for the catalytic activity was 7.25 and the apparent temperature optimum was 313 K. The Km value was 2.9 X 10(-5) M with FDP as substrate, and 2.8 X 10(-3) M with F1P as substrate. The thermal stability of this pig muscle enzyme was higher than that of the rabbit muscle enzyme. The thermal inactivation of the pig aldolase did not show simple first-order kinetics. The higher conformational stability of the pig aldolase than that of the rabbit enzyme was demonstrated by its higher resistance to the denaturing effect of urea.