Abstract: The productive biology of hard clam ( Meretrix meretrix Linnaeus ) cultured in South Zhejiang was studied by means of histological section in this paper. The reproducitive cycle , fatness , gonad development , breeding season of M . meretrix cultured in south Zhejiang are described. The reproductive cycle of M. meretrix was divided into 5 stages : proliferation stage , growing stage , maturation stage , breeding stage and suspensive stage. The spawning season was from late May to mid2August (21. 8 -31. 0 ℃) , and the peak of spawning occurred from late June to late July when the temperature was about 25 -30 ℃. The highest index of fatness on averagewasabout8.84%inJune,andthelowestwasabout3.21%inJanuary. Thesexsualmaturityat1year old M. meretrix was found. The relationship of full maturation and spawning with accumulated temperature is discussed in this paper.