Sidney Austin Riley (18 April 1878 – 31 March 1964) was a rugby union player who represented Australia.

Riley, a centre, was born in Auckland, New Zealand, and claimed one international rugby cap for Australia, against New Zealand, at Sydney, on 15 August 1903. He also played rugby league in a match for New Zealand against Auckland and played for Auckland several times and was a member of the Ponsonby rugby club and Ponsonby United rugby league club.