Abstract We compared the diet of larval Japanese sardine Sardinops melanostictus between the western and eastern areas of the Japanese coastal waters of the Sea of Japan in March–May 2019–2022. Standard lengths of larvae examined for gut contents ranged from 5 to 17 mm; in both areas, the main prey items found in the gut were copepod nauplii and copepodites. However, food incidence was low in eastern areas, and mean prey width differed between the areas. Larvae in the western area in March and April fed on copepods as large as the largest in ambient waters, such as the copepodites of Paracalanus spp. and the nauplii of large Calanoida, whereas the main food for larvae in the eastern area in May was small copepod nauplii such as those of Oithona spp. These differences suggest that the prey environment in the western area in March and April is more favorable for sardine larvae than in the eastern area in May. Understanding such spatial patterns in prey availability and larval diets would be essential for elucidating the survival and recruitment processes of Japanese sardine in the Sea of Japan.