A control system for an engine is provided, which includes an engine body formed with a cylinder, a NOx catalyst, an oxidation catalyst, a PM filter, a fuel injector configured to perform a main injection and a post injection, and a controller configured to execute a DeNOx control in which the fuel injector is controlled to perform the main and post injections so that an air-fuel ratio of exhaust gas is brought close to the stoichiometric air-fuel ratio or becomes rich and fuel supplied into the cylinder by the post injection combusts therein, and a filter regenerating control in which the fuel injector is controlled to perform the main and post injections so that the air-fuel ratio becomes lean and the fuel supplied into the cylinder by the post injection causes no combustion therein, the controller executing the DeNOx control and the filter regenerating control consecutively in this order.