An exhaust gas control system for an internal combustion engine (1) includes: a first catalyst (4a) disposed on an exhaust passage for the internal combustion engine (1), the first catalyst (4a) being a NOx storage reduction catalyst; a second catalyst (6) disposed on the exhaust passage at a position downstream of the first catalyst (4a), the second catalyst (6) being a NOx selective catalytic reduction catalyst; a first NOx sensor (N2) mounted on the exhaust passage at a position between the first catalyst (4a) and the second catalyst (6); a second NOx sensor (N3) mounted on the exhaust passage at a position downstream of the second catalyst (6); and an electronic control unit (10). The electronic control unit (10) is configured to evaluate NOx reducing performance of the second catalyst (6) based on a value detected by the first NOx sensor (N2) and a value detected by the second NOx sensor (N3), when an evaluation condition is satisfied.