Abstract: Eriocheir leptognathus is widely distributed in brackish waters from Fujian province to the eastern coast of Korea peninsula,especially abundant in Changjiang estuary. Its larval morphological characteristics,breeding season and larval living environment are similar to those of E. sinensis. The megalops of two species are difficult to be distinguished from each other in the natural waters,so that farmers suffer economic loss in crab culture due to misidentification. It is necessary to investigate the larval development of E. leptognathus. This paper deals with the complete larval development of E. leptognathus,describes the larvae reared in the laboratory in detail. The berried females of E. leptognathus are obtained from Sanjia seaport of Shanghai. The larval culture is carried out under the temperature of 18—25℃,salinity of 18‰—20‰ and photo intensity of 200—600lx. Under these conditions,E. leptoganathus passes 5 zoeal stages before metamorphosis to the megalopal stage. The megalopa and crab I instar are attained in minimum 15 and 23 days after hatching,respectively. Morphological characteristics of the first zoea and megalopa of E. leptognathus are compared with those of E. sinensis. The first zoea of the two species can be easily distinguished from each other by the form of the second antenna and the knobs of the abdominal somites. The exopode of the second antenna of E. leptognathus is about 1/15 in length of protopodal process and has two approximately equal simple setae on terminal,while of E. sinensis is about 1/3—1/2 in length of protopodal process and has two unequal spines near the distal end. There are 2 pairs of dorso-lateral knobs on the second to third abdominal somites of E. leptognathus while there are 3 pairs on the second to fourth abdominal somites of E. sinensis. The main difference of the two species megalopae exists in body length,the shape of rostrum,dactylus of pereiopods 2—4. the plumose setae on exopods of pleopods,setation of other appendages and of telson. Sakai treated it as another genus Neoeriocheir,which is supported by Guo et al. Dai aiyun and Qiu gaofeng considered that E. leptognathus belongs to Eriocheir. There are denticles on rostral,dorsal spines on the carapace of the first zoea,and there are two indistinctly round lobs on the postero-dorsal carapace of the megalopa of E. leptognathus,which are considered as the typical characteristics of the larvae of Eriocheir from other genuses.