The Rochester by-election, 1903 was a parliamentary by-election held in England in September 1903 for the House of Commons constituency of Rochester in Kent.
The vacancy was caused when the borough's Conservative Member of Parliament (MP), known by his courtesy title as Viscount Cranborne, succeeded to the peerage on 22 August 1903. He had been MP for Darwen from 1885 to 1892, and then for Rochester since winning the seat at a by-election in 1893.
Cranborne had been returned unopposed at the 1900 general election, so the borough had not seen a contested parliamentary election since 1895.
The two major parties chose their candidates on 2 September. The Unionists (the Conservatives and their Liberal Unionist allies) chose Charles Tuff, the owner of a large firm of contractors. He had been mayor of Rochester from 1900 to 1902.
The Liberal Party selected as its candidate Sir Harry Johnston, an African explorer and colonial administrator.
The writ for the by-election was received on 15 September by the mayor, who fixed 18 September as the closing day for nominations, and Wednesday 23 September as polling day. No independent or minor party candidates were nominated, so the election was a two-way contest between Tuff and Johnston.