For elucidation of the population dynamics and efficient use of the fisheries resource of Pacific rainbow smelt Osmerus dentex, we examined the appropriate age assessment method and growth trajectory of this species. Samples were collected with an otter trawl net along the sea-bottom in Funka Bay from October 2018 to September 2019 and a scoop net for spawners at the mouth of the Yamazaki River in late April to mid May in 2019. Coefficient of variation and average percentage error of three readers by sagittal otolith reading (12.4% and 9.3%, respectively) were lower (better) than scale readings (15.1% and 11.4%). Percentage of agreement among three readers for otolith (41.2%) was higher than for scale (17.7%). Opaque margins in otoliths were found from March to August with the peak in April and May around the spawning period implying that the increments were formed annually. Maximum age was 6.8 years and the largest body size was 269 mm SL. O. dentex caught in this study area showed faster growth by growth performance index ϕ’ than those in other areas, and this growth difference might be caused by the response to latitudinal effects.