The early development characteristics of Tanakia chii larvae and juveniles were observed on the artificially fertilized and hatched fish. Newly hatched larva contained a substantial amount of yolk, with pale yellow in color and tiny tubercles on the surface. On day 3, a pair of hilly projections of yolk expanded toward both sides of the body, and the primordial fin-fold at the caudal portion developed. Optic cups developed into circular on day 6. Lens and melanin pigments began to form on the optic cups on day 8. On day 11, the mouth formed and brain developed, and melanophores were observed on the body. On 15 days old larvae, the branchial groove and anus had developed, the base of dorsal fin and anal fin formed, and caudal fin rays formed at the lower lobe. On day 21, the boundary of the head and trunk was clear, the gas-bladder divided into anterior and posterior lobes. The numbers of the dorsal fins and anal fins were 8 and 10 respectively. Even though the larva still had partial yolk-sac left, it started to eat to replenish energy, and the larvae began free swimming since then. During day 31 to day 36, rudiments of the pectoral fin appeared as small membranes, and some rays were formed in the pelvic fin. The caudal fin changed from a truncated to a deep forked shape. In 61 -63 days old juvenile, scales appeared on the body and a black longitudinal line appeared on the middle and latter parts of body. Since then, the fish always swam as a cohort. The growth curve of body length could divide into two stages: the growth rate was relatively slow from 1 to 21 days after hatching, and the growth rate was higher from 21 to 81 days old. We consider day 21 might be the age when Tanakia chii swims out of the mussels because we observed the larvae began to eat at that time. Furthermore, development of sensing organ, feeding, breathing and swimming apparatus is rapid in the early life stage of Tanakia chii, which may be important in providing the larvae with ability to cope with external environment and improve their survival rate after the larvae swim out the host mussel.