The feeding of mature threespine stickleback Gasterosteus aculeatus L. was studied during the entire spawning period (late May – early July) in 2016 at three locations in the mouth of Chupa Inlet, Gulf of Kandalaksha, White Sea. The fish mostly feed on benthos: stickleback eggs (up to a half of stomach content), pupae and larvae of Chironomidae, Polychaeta and A mphipoda, as well as imagoes of Diptera. In good spawning grounds with a high density of spawners, the proportion of stickleback eggs in the diet is higher. The effects of sex, spawning stage and location were determined. Females, in comparison with males, have a more diverse diet (20 food items versus 13) and show greater changes during the spawning season, in particular, they consume energetically richer food items. This is likely because the more territorial males, occupied with guarding the progeny, are more limited in their diet modification possibilities. Differences between the sexes are especially high by the end of the spawning period. Females begin intensive post-spawning feeding earlier than males, who have to guard the nests. We also observed a decrease of the condition factor during the spawning period, which is probably associated with high energetic costs of spawning.