  String theory generically predicts the coupling between the Affleck-Dine
field and axion field through higher-dimensional operators. We thus explore the
Affleck-Dine baryogenesis on an axion background. It turns out that the axion
oscillation produces an enough amount of baryon asymmetry of the Universe just
after the inflation, even without a soft supersymmetry-breaking $A$-term. This
baryogenesis scenario is applicable to the string axion inflation.
