Renfrew South was a federal riding represented in the House of Commons of Canada from 1867 to 1968.

The South Riding initially consisted of the townships of McNab, Bagot, Blithfield, Brougham, Horton, Adamston, Grattan, Matawatchan, Griffith, Lyndoch, Raglan, Radcliffe, Brudenell, Sebastopol, and the villages of Arnprior and Renfrew.

In 1872, the townships of Hagarty, Richards, Sherwood, Burns and Renfrew, Jones, were added to the South Riding.

In 1924, "Renfrew South" was defined to consist of the part of the county of Renfrew lying south of and including the townships of Richards, Haggarty, Brudenell, Sebastopol, Grattan, Admaston and Horton, and including the part of the village of Eganville that lies in the township of Grattan.

In 1952, it was defined to consist of the part of the county of Renfrew lying south and west of and including the townships of Richards, Hagarty, Algoma South, Grattan, Admaston and Horton, the part of the village of Eganville lying within the township of Grattan, and, in the territorial district of Nipissing, the townships of Airy, Murchison, Dickens, Sabine, and Lyell.