Abstract: Stage-specific differences in the diel vertical distribution and migration of a euphausiid, Euphausia pacifica, were studied at a single station (E2, 70m water depth) in the South Yellow Sea, by sampling with a conical closing net from five discrete strata, every 3h, for 24h, on 2–3 May 2001. Environmental data were collected simultaneously with the net sampling. Results showed that eggs contributed a large proportion of the numerical abundance of the Euphausia pacifica population throughout the investigation. They were mainly distributed below 20m depth, and concentrated in the 30–50m strata throughout the day and night. Nauplius stage I (NI) was distributed below 10m, and seldom occurred in the upper 10m. Nauplius stage II (NII) and Metanauplius stage (MN) extended their distribution to nearly the whole water column; however, the MN resided somewhat shallower than NII. The majority of calyptopis stages I to III (CI to CIII ) and early furcilia stages I to III (FI to FIII) were restricted to the upper 30m throughout the day. The weighted mean depth tended to increase as the stage progressed from stage FI onward. Calyptopis stages showed a weak or moderate diel vertical migration behavior, and the onset of an obvious diel vertical migration took place in FII stage. The amplitude of the diel vertical migration varied with developmental stages. Stages after FIV were often absent from samples during the investigation, but from the limited available data, DVM occurred from stages FIV–VI and female adults. However, the male adults showed a somewhat different migration behavior. In summary, an ontogenetic migration pattern is obvious from this high-frequency sampling: spawning took place at 20–50m depth, hatched nauplii sank a little, metanauplius began moving toward the surface, and calyptopis larvae reached the uppermost layer. Furcilia larvae began DVM and deepened their daytime residence depth with age. The vertical distribution of Euphausia pacifica seemed to relate to temperature and chlorophyll a. [Copyright &y& Elsevier]