Sydney Francis Foster (March 23, 1893 Cazenovia, Madison County, New York – November 21, 1973) was an American lawyer and politician.
Afterwards he practiced law in Liberty, and was elected District Attorney of Sullivan County, New York, in 1925.
In 1954, he ran on the Republican ticket for the New York Court of Appeals, but was defeated by Democrat/Liberal Adrian P. Burke.
On January 1, 1960, Foster was appointed to the Court of Appeals by Governor Nelson A. Rockefeller to fill the vacancy caused by the election of Charles S. Desmond as Chief Judge.
In November 1960, Foster he ran on the Republican and Liberal tickets to succeed himself, and was elected.