The changing regularity of calcium and magnesium ion contents and activity of phospholipase C (PLC) in integument of molting silkworm (Bombyx mori) larvae, and the mutual balance of ions were determined and analyzed by at. absorption spectrometry (AAS) and enzyme-linked immune assay (ELISA).Results indicated that Ca2+ content reached peak value upon completion of molting in each instar.However, this peak value decreased with larval age.For example, Ca2+ mass ratio in the newly exuviated larvae of the 3rd instar was 8.2815 mg/g, while that of the 4th instar was 6.2835 mg/g and that of the 5th instar was 5.1335 mg/g.Moreover, Ca2+ content in integument of young larvae was generally higher than that of grown larvae.The similar trend of Mg2+ contents was found in different larval instars with the highest value (0.6123 mg/g) detected only in newly exuviated larvae of the 3rd instar.Mg2+ content had a small scale concussion rise before molting of each instar.The activity of PLC achieved peak value (38.2 to 41.0 U/mL) before molting of each instar, sustained to the middle of molting, and fell down gradually to low values (21.0 to 29.2 U/mL).It increased again after completion of ecdysis.PLC activity was at relatively low level from the 5th instar to the pre-pupa stage.Interestingly, an increasing of Mg2+ content was found to coincide with the decreasing of Ca2+ content in every instar, and the time point of coincidence was postponed with the development of silkworm larvae.