In this research, reproduction time and larval development of Anodonta cygnea in Lake Cildir during 2000-2002 were studied. The mean number of larvae (N) produced by each gravid female was about 115,000 and the mean shelf length was (L) 99 mm (59.2-128.3). Best fitted relationship between the number of larvae and mussel length was found as N 43,696*L(1.68) (n = 34, r = 0.42). There was a weak relationship between the length of the Mussel and the weight of gills full of., larvae, as W = 0.0007 L(1.958), r = 0.68 (P<0.01). The weakest relationship Was found between length (LL) and height (HL) of larvae: HL = 0.2682LL + 256.47 (r = 0.23) (P<0.05). The duration of gravidity was observed from the end of July to June the following year.