By exposure to 12×10-3mol/dm3K+ for 24h, more than 90% of planktonic larvae of Babylonia formosae and B. areolata were effectively induced to metamorphose completely. 15×10-3mol/dm3K+exerted toxic effect on larval B. areolata over a 24-h period, but produced better results of induction by 12h exposure. Metamorphosed juveniles induced by increased by K+could move and feed normally. Percent metamorphosis increased with average shell height for K+-induced larvae. L-DOPA, epinephrine and norepinephrine ranging from 5.5×10-6 to 5.5×10-5mol/dm3 had no inductive activity to metamorphosis in larval B. areolata, whereas the rate of metamorphosis induced by dopamine at a concentration of 10-4mol/dm3 was approximately half less than that by 12×10-3mol/dm3K+. TEA (a K+-channel blocker) did not inhibit metamorphosis in the two Babylonia larvae by induction of K+. Based on the results of K+-induced experiments, it is preliminarily suggested that shell height of larvae achieving metamorphic competence was in the range of 860.2～1009.8μm for B. fbrmosae, and 849.6～956.0μm for B. areolata. In addition, planktonic larvae of the two Babylonia had delayed metamorphosis.