Abstract: 【Aim】 Rice leaffolders are among the most important pests of rice crops， and mainly include Cnaphalocrocis exigua and C. medinalis in China. Because only a few studies have been done on C. exigua and the two species have similar morphology and habits， they are generally confused. The study aims to reveal the morphological characteristics distinguishing C. exigua from C. medinalis.【Methods】 The morphological characteristics of larvae， pupae and adults of C. exigua and C. medinalis larvae were described， the reproductive systems of male and female adults of C. exigua were dissected， and the morphological differences between C. exigua and C. medinalis were compared. 【Results】 For C. exigua， the sclerite numbers of prothorax， mesothorax and metathorax， and abdomen in larva are 2， 12 and 5， respectively， which are arranged into 1， 3 and 2 rows， respectively. There is a finger-shape process at the terminal end of pupal abdomen， which bears 8 setae. Forewing is yellowish， with brown bands.  The band in the costal margin is wide, while the longitudinal band in the outer margin is C-shaped. Transverse anterior line and transverse posterior line are parallel with each other and the median line reaches the posterior margin of forewing. Male testis is golden yellow， and accessory glands and ejaculatory ducts are long but deferent ducts and seminal vesicles are short. The weakly sclerotized male valva is densely covered with long hair. There are two sclerotized thorns in the vesica of aedeagus. The female ovary is short， the length of the lateral oviducts and the common oviduct are similar， and bursa copulatrix is long. The color of sclerites in thorax and the arrangement of sclerites in mesothorax and metathorax can be used to identify the larvae of C. exigua from C. medinalis. The color of forewing， the shape and the length of bands in forewing， the arrangement of transverse anterior line and transverse posterior line， the sclerotization of valva and the sclerotized zone in the vesica can be used to identify the adults of C. exigua from C. medinalis. 【Conclusion】 The results can be used for the accurate identification of larvae and adults of C. exigua and C. medinalis， providing a basis for the accurate forecast of C. medinalis.

Key words: Cnaphalocrocis exigua, Cnaphalocrocis medinalis, larva, adult, morphology, reproductive system