A road surface condition-detecting system for a vehicle detects a road surface condition from road noise generated by a vehicle wheel. The road surface condition is determined based on parameter data of frequency components of the road noise, by a neural network. The road noise may be corrected by eliminating therefrom a disturbance, such as audio output and exhaust noise. A present state of the road surface condition may be determined based on at least two consecutive determinations made based on the road noise detected at regular time intervals. Exclusive neural networks may be used for respective road surface condition types. One of a plurality of neural networks provided for respective vehicle speed ranges may be selected according to an actual vehicle speed. Detected sound pressure levels of the road noise extracted by frequency analysis may be normalized within respective ranges defined by upper and lower limits set corresponding to predetermined frequency ranges before being supplied to the neural network.