An exhaust gas control system for an internal combustion engine, the exhaust gas control system comprising: a first catalyst disposed on an exhaust passage for the internal combustion engine, the first catalyst being a NOx storage reduction catalyst; a second catalyst disposed on the exhaust passage at a position downstream of the first catalyst, the second catalyst being a NOx selective catalytic reduction catalyst; a first NOx sensor mounted on the exhaust passage at a position between the first catalyst and the second catalyst, the first NOx sensor being configured to detect a concentration of NOx in exhaust gas flowing into the second catalyst; a second NOx sensor mounted on the exhaust passage at a position downstream of the second catalyst, the second NOx sensor being configured to detect a concentration of NOx in the exhaust gas flowing out of the second catalyst; and an electronic control unit configured to, when an evaluation condition is satisfied, evaluate NOx reducing performance of the second catalyst based on a value detected by the first NOx sensor and a value detected by the second NOx sensor, the evaluation condition being a condition that NOx is supplied to the second catalyst of which a temperature is within an activation temperature range and on which a reductant in an amount equal to or larger than an adsorption amount predetermined value has been adsorbed, and the NOx supplied to the second catalyst being NOx that has been desorbed from the first catalyst due to an increase in a temperature of the first catalyst, the first catalyst storing NOx, up to a temperature equal to or higher than a desorption temperature at which desorption of NOx from the first catalyst starts. a first catalyst disposed on an exhaust passage for the internal combustion engine, the first catalyst being a NOx storage reduction catalyst; a second catalyst disposed on the exhaust passage at a position downstream of the first catalyst, the second catalyst being a NOx selective catalytic reduction catalyst; a first NOx sensor mounted on the exhaust passage at a position between the first catalyst and the second catalyst, the first NOx sensor being configured to detect a concentration of NOx in exhaust gas flowing into the second catalyst; a second NOx sensor mounted on the exhaust passage at a position downstream of the second catalyst, the second NOx sensor being configured to detect a concentration of NOx in the exhaust gas flowing out of the second catalyst; and an electronic control unit configured to, when an evaluation condition is satisfied, evaluate NOx reducing performance of the second catalyst based on a value detected by the first NOx sensor and a value detected by the second NOx sensor, the evaluation condition being a condition that NOx is supplied to the second catalyst of which a temperature is within an activation temperature range and on which a reductant in an amount equal to or larger than an adsorption amount predetermined value has been adsorbed, and the NOx supplied to the second catalyst being NOx that has been desorbed from the first catalyst due to an increase in a temperature of the first catalyst, the first catalyst storing NOx, up to a temperature equal to or higher than a desorption temperature at which desorption of NOx from the first catalyst starts.