The characteristics of incubation time, yolk absorption, onset of feeding, and early larval growth of the Japanese sand eel Ammodytes personatus was examined. Incubation time to the beginning of hatching and to the time of 50% hatching was, respectively, 14 days and 20 days at 15.5°C, 18 days and 25 days at 10.5°C and 33 days and 51 days at 6.5°C. Eggs showed amarkedly extended period of hatching, 12, 29, and 59 days at each of the above respective tempera tures. Using the relationship between incubation time and temperature, the spawning season was estimated to be from mid-December to the end of January with a peak at the end of December. Newly hatched larvae commenced feeding at an age of 2 days and all larvae completed yolk sac absorption by 12 days at 6.5°C, indicating a long overlapping period of endogenous and exogenous nutrition. The average size of newly hatched larvae is 4.72 mm in standard length and 33.9 μg in dry weight. The specific growth of larvae up to 24 days old fed with field-collected microplankton and rotifier in the ratio 2:8 at 6.5°C was 4.2 % per day in dry weight.