Geranial is one of the potent odor compounds in fresh ginger. To clarify the generation of geranial in ginger, the alcohol dehydrogenase activity was measured in a crude enzymatic system of ginger. This enzyme solution was found to contain geraniol dehydrogenase (GeDH) specifically acting on geraniol as a substrate with NADP as a coenzyme. Geranial generation and GeDH activity were investigated for different maturity stages and storage periods of ginger. Both were at maximum levels from just after harvesting to initial storage. The GeDH activity subsequently dropped, and the generation of geranial also stopped. These results suggest that the GeDH activity in ginger is related to the generation of geranial.