In order to recognize the ontogeny in morphological characteristics and its application in the classification of fish larvae and juveniles in genus Diogenichthys Bolin, 1939, larvae and juveniles samples collected during the oceanographical expedition cruises were identified separately based on the literatures related to the morphological and taxonomic features of this genus. The cruises were conducted in the Kuroshio extension region of the East China Sea during April to July 1984, December 1984 to January 1985, and April to June 1985 separately. It aimed to enrich the knowledge on the early life history stage in China and to provide available information to resolve taxonomic problems of these species in the related marine ecological investigations. Based on the classification and identification works, larvae and juvenile fish of D. atlanticus (T?ning, 1928), D. panurgus Bolin, 1946 and D. laternatus (Garman, 1899) in genus Diogenichthys were identified separately. Ontogenic morphological characteristics for the three species were described in some detail. Moreover, a brief key for classification of these species was established. The observed result conveyed that as most other species in the order Myctophiforme, larvae and juveniles fish in genus Diogenichthys own the unique organ of photophores. However, sequence and numbers of photophores formation in larvae of three species of Diogenichthys were different. There were 6 photophores formed at the end of development in D. atlanticus. Br2 on the branchiostegal organ was first observed in the postlarval stage at 5.10 mm in standard length; PO2 on the pectoral organ was first observed in the juvenile stage at 7.60 mm; PO5 on the pectoral organ was first observed at the juvenile stage at 8.10 mm, and three photophores on the postero-anal organ, AOp1、AOp2 and AOp3 were first observed in the juvenile stage at 10.0 mm in standard length. In D. panurgus, there were 27 photophores formed at the end of development. Br2 on the branchiostegal organ and PO5 on the pectoral organ were first observed in the juvenile stage at 6.40 mm in standard length; and then Dn on the dorso-nasal organ, Br1 and Br3 on the branchiostegal organ, Op1 and Op2 on the opercular organs, PLO on the suprapectoral organ, PVO1 and PVO2 on the subpectoral organ, PO1-4 on the pectoral organ, SAO3 on the supra-anal organ, VO1-4 on the ventral organ, AOa1-5 on the antero-anal organ, and AOp1-3 on the postero-anal organ could be observed in the juvenile stage at 12.0 mm in standard length. In D. laternatus, there were 2 photophores formed at the end of development. Br2 on the branchiostegal organ was first observed in the postlarval stage at 5.25 mm in standard length, PO5 on the pectoral organ was first observed in the postlarval stage at 6.60 mm. When considered to the other developmental characteristics, a column of chrysanthemum-shaped melanophores distribute at the ventro-margin side above anal fin in larvae and juveniles fish of D. atlanticus, D. panurgus and D. laternatus separately. And this morphological characteristic is a commom feature in the genus Diogenichthys. D. atlanticus larvae own a barbell which projects from the anterior tip of the lower jaw; and have a cluster of melanophores, which was as large branched or starry or radiate or small chrysanthemum shaped, scattered at ventro-lateral side above the anus. However, neither D. panurgus nor D. laternatus larvae own a barbell at the anterior tip of the lower jaw, and have melanophores scattered at ventro-lateral side above the anus. There is a melanophore at the anterior tip of the lower jaw in D. panurgus larvae, but no such melanophore is found on that of D. laternatus larvae.