Sidney Oslin Smith Jr. (born 1923) is a former United States federal judge.
Born in Gainesville, Georgia, Smith received an A.B. from Harvard College in 1947 and an LL.B. from the University of Georgia School of Law in 1949. He was in private practice in Gainesville, Georgia from 1949 to 1962. He was an Assistant solicitor general of Northeastern Judicial Circuit of Alabama from 1951 to 1961.
On August 24, 1965, Smith was nominated by President Lyndon B. Johnson to a seat on the United States District Court for the Northern District of Georgia vacated by William Boyd Sloan. Smith was confirmed by the United States Senate on September 10, 1965, and received his commission the same day. He served as chief judge from 1968 until his resignation from the bench on June 1, 1974, Smith then returned to private practice, in Atlanta, Georgia.