A method for controlling a hybrid vehicle, the hybrid vehicle having an internal combustion engine that is capable of changing a combustion mode between a stoichiometric combustion mode in which a stoichiometric air-fuel ratio is set as a target air-fuel ratio and a lean combustion mode in which a lean air-fuel ratio is set as the target air-fuel ratio and a motor that is capable of performing assist of power of the internal combustion engine by a power running operation, the method comprising: previously setting a stoichiometric combustion operating region where the stoichiometric combustion mode is set and a lean combustion operating region where the lean combustion mode is set with torque and rotation speed of the internal combustion engine being parameters; as a boundary at a high torque side between the both operating regions, setting a second boundary (L2) at which a change from the stoichiometric combustion mode to the lean combustion mode is executed when the torque decreases at a low torque side as compared with a first boundary (L1) at which a change from the lean combustion mode to the stoichiometric combustion mode is executed when the torque increases; characterized in that the method further comprises, upon shift from the stoichiometric combustion operating region to the lean combustion operating region by crossing the second boundary (L2), after changing the combustion mode, for delay in change of an intake-air quantity which is associated with the combustion mode change, performing a quantity-decrease correction of a fuel injection quantity so as to maintain the target air-fuel ratio at the lean air-fuel ratio, and performing the assist by the motor so as to attain a required driving force; and setting the second boundary (L2) so that the assist can be performed within a range of a maximum output of the motor. previously setting a stoichiometric combustion operating region where the stoichiometric combustion mode is set and a lean combustion operating region where the lean combustion mode is set with torque and rotation speed of the internal combustion engine being parameters; as a boundary at a high torque side between the both operating regions, setting a second boundary (L2) at which a change from the stoichiometric combustion mode to the lean combustion mode is executed when the torque decreases at a low torque side as compared with a first boundary (L1) at which a change from the lean combustion mode to the stoichiometric combustion mode is executed when the torque increases; characterized in that the method further comprises, upon shift from the stoichiometric combustion operating region to the lean combustion operating region by crossing the second boundary (L2), after changing the combustion mode, for delay in change of an intake-air quantity which is associated with the combustion mode change, performing a quantity-decrease correction of a fuel injection quantity so as to maintain the target air-fuel ratio at the lean air-fuel ratio, and performing the assist by the motor so as to attain a required driving force; and setting the second boundary (L2) so that the assist can be performed within a range of a maximum output of the motor. <EOS>