Intake air control system and method for an internal combustion engine

An intake air control system for an internal combustion engine (1) is provided which comprises an intake throttle valve (8) that controls an intake air quantity of air flowing into the engine (1), an EGR valve (10) that controls a quantity of exhaust gas recirculated back to a portion of an intake system of the engine (1) downstream of the intake throttle valve (8), and a control unit (20, FIGS. 2 to 13) that controls the intake throttle valve (8) and the EGR valve (10) in accordance with an operating condition of the engine (1). The control unit (20) includes a target opening area calculating section (FIGS. 2, 8 to 13) that calculates a target opening area of the intake throttle valve (8) based on a target EGR ratio corresponding to the operating condition of the engine (1), and a control section that controls an opening degree of the intake throttle valve based on the target opening area. An intake air control method is also provided.