An engine control system for a vehicle, which is configured to control an engine using a plurality of control modes, comprising: a controller configured to selectively set a first control mode or a second control mode and to control the engine using the set control mode, the first control mode and the second control mode being provided such that the engine is operable with a smaller fuel amount in the second control mode than in the first control mode; and a mode switching device for switching the control mode set in the controller between the first control mode and the second control mode; wherein the mode switching device includes an operation member which is operated by a driver, wherein the controller is configured to determine that the command for switching the control mode has been input only when an operation time for which the operation member is operated by the driver falls within a predetermined time range which is not less than a predetermined first time and not more than a predetermined second time, wherein the controller is configured to determine that a command for switching the control mode is valid if a predetermined driving condition is met, in response to the command input to the mode switching device, and to determine that the command is invalid if the predetermined driving condition is not met, in response to the command input to the mode switching device characterized in that the engine control system comprises an acceleration determiner configured to determine whether or not the vehicle is driving with a predetermined acceleration, a driving power transmission determiner configured to determine whether or not a transmission path of a driving power generated in the engine is disconnected, and a gear position sensor for detecting a gear position of a transmission mounted in the vehicle; in that the predetermined driving condition includes a first condition that the vehicle is driving with an acceleration less than the predetermined acceleration, and a second condition that the transmission path is disconnected or the gear position detected by the gear position sensor is a gear position corresponding to a reduction gear ratio less than a predetermined reduction gear ratio which is not more than a maximum reduction gear ratio; and in that the predetermined driving condition is met when the first condition and the second condition are met. a controller configured to selectively set a first control mode or a second control mode and to control the engine using the set control mode, the first control mode and the second control mode being provided such that the engine is operable with a smaller fuel amount in the second control mode than in the first control mode; and a mode switching device for switching the control mode set in the controller between the first control mode and the second control mode; wherein the mode switching device includes an operation member which is operated by a driver, wherein the controller is configured to determine that the command for switching the control mode has been input only when an operation time for which the operation member is operated by the driver falls within a predetermined time range which is not less than a predetermined first time and not more than a predetermined second time, wherein the controller is configured to determine that a command for switching the control mode is valid if a predetermined driving condition is met, in response to the command input to the mode switching device, and to determine that the command is invalid if the predetermined driving condition is not met, in response to the command input to the mode switching device characterized in that the engine control system comprises an acceleration determiner configured to determine whether or not the vehicle is driving with a predetermined acceleration, a driving power transmission determiner configured to determine whether or not a transmission path of a driving power generated in the engine is disconnected, and a gear position sensor for detecting a gear position of a transmission mounted in the vehicle; in that the predetermined driving condition includes a first condition that the vehicle is driving with an acceleration less than the predetermined acceleration, and a second condition that the transmission path is disconnected or the gear position detected by the gear position sensor is a gear position corresponding to a reduction gear ratio less than a predetermined reduction gear ratio which is not more than a maximum reduction gear ratio; and in that the predetermined driving condition is met when the first condition and the second condition are met.