The 2003 Senior British Open was a senior major golf championship and the 17th Senior British Open, held from 24–27 July at Turnberry in South Ayrshire, Scotland. It was the 5th Senior British Open played at the course and the first Senior British Open played as a senior major championship.

Tom Watson defeated Carl Mason in a playoff to win his first Senior British Open title and his second senior major championship victory.

The 2003 event was the 5th Senior British Open played at Turnberry.

The field consisted of 144 competitors: 139 professionals and 5 amateurs.

18-hole stroke play qualifying rounds were held on Monday, 21 July, on two places in Scotland, the Barassie Links in Kilmarnock and the Kintyre course at Turnberry, for players who were not already exempt. The 31 leading players from the qualifying competitions joined the 113 exempt players for the championship.

77 players made the 36-hole cut, 76 professionals and one amateur. Arthur Pierce, Ireland, finished leading amateur at tied 62nd.

The field included five former winners of The Open Championship. Four of them made the cut; 1975, 1977, 1980, 1982 and 1983 Open champion Tom Watson (won), 1966, 1970 and 1978 Open champion Jack Nicklaus (tied 14th), 1963 Open champion Bob Charles (tied 20th) and 1959, 1968 and 1974 Open champion Gary Player (tied 51st). 1961 and 1962 Open champion Arnold Palmer did not make the cut.

The field also included three former runners-up at The Open Championship; Tom Kite (4th), Rodger Davis (tied 27th) and Simon Owen (tied 32nd).