It is generally believed that the hippocampus plays a crucial role in declarative memory—remembering facts and events—but not in gradual stimulus-response association or incremental value learning. Based on the finding that CA1 conveys strong value signals during dynamic foraging, we investigated the possibility that the hippocampus contributes to incremental value learning. Specifically, we examined effects of inactivating different subregions of the dorsal hippocampus on behavioral performance of mice in a dynamic two-armed bandit task. A reinforcement learning model-based analysis indicated that inactivation of CA1, but not dentate gyrus, CA3, or CA2, impaired trial-by-trial updating of chosen value without affecting value-dependent action selection. As a result, it took longer for CA1-inactivated mice to bias their choices toward the higher reward-probability target after changes in reward probability. Further analyses indicated that the effect of CA1 inactivation on value learning could not be accounted for by an impairment in episodic control of choice behavior, estimating the time of reward probability change, or behavioral inhibition. Our results indicate, contrary to the traditional view, that the hippocampus, especially CA1, might contribute to incremental value learning under certain circumstances.