Abstract: A knocking control system for an internal combustion engine with the inlet valves and exhaust valves having valve timing thereof controlled depending on operating conditions of the engine. It is determined whether or not knocking has occurred in the engine on the basis of a detection parameter indicative of knocking and at least one discrimination parameter. The operation of the engine is controlled by the use of at least one control parameter in response to the determination result. The values of the discrimination and control parameters arfe selected in accordance with the actual valve timing. The detection parameter is a level of vibration of the engine comprising a noise component and a knocking component. It is determined that knocking has occurred when the level of the knocking component is higher than one knocking discrimination level set based on the level of the noise component and the discrimination parameter irrespective of the actual valve timing.