Abstract: The activity of adenylate cyclase in Schistosoma japonicum was assayed by radiometric raethod. The 3H-cAMP formed during enzymatic reaction was separated from substrate 3H-ATP by a short Dowex 1×2 (100-200 mesh) 0.5×3 cm column, then the radioactivity of 3H-cAMP was determined by liquid scintillation measurement.The optimum pH of the enzyme activity in S. japonicum homogenate is 7.5. Both male and female worms possess almost the same activity, which increases with the age between 20 to 48 days. The enzyme activity of 40-day-old adult worm was 80000 ± 3000 cpm/pair worm-minute. The activity of adenylate cyclase on the surface membrane of the male worm was one-fold higher than that of the female.3.3× 10-4M of nithrocyamine, metrifonate and niridazole had no effect on the activity of adenylate cyclase in S. japonicum homogenate. 3.3×10-M of furapromidum showed a slight inhibition, whereas saturated pyquiton inhibited 50% activity of the enzyme on the surface membrane of the worm.