Mayflower Theatre (formerly the Gaumont Theatre and originally the Empire Theatre) is a Grade II listed theatre in the city centre of Southampton, England, with a capacity of 2,300. It features West End theatre shows when they tour the United Kingdom. In addition to this, one-off comedy shows and music events often take place at the theatre too.

It is the largest theatre in South England outside of London, being more than twice as large as Brighton's Theatre Royal and four times as large as Bristol's Old Vic.

The theatre opened on 22 December 1928 as The Empire Theatre, part of the Moss Empire theatre group. It was part of the company's expansion of the late 1920s which also saw theatres constructed in Edinburgh, Glasgow, Liverpool, Oxford and The Dominion, in London.

At the time of construction, it was the largest theatre in the south of England, a title it still holds. In the early days, many shows were transported by train. The theatre's proximity to Southampton Central railway station made its location ideal, but meant that many shows were not as spectacular as their London counterparts. The theatre suffered in early days, to the arrival of cinema, with sound or 'talkies'. This led to the 1933 installation of a projection box in the balcony and a screen, which could be raised and lowered at the front of the stage. By 1942, the theatre was mainly used as a cinema and was taken over by The Gaumont-British Picture Corporation.

As part of the Rank Organisation, the theatre has hosted concerts by many famous artists, including Bill Haley & His Comets in 1957, the Beatles in 1963, the Rolling Stones supported by Ike & Tina Turner and The Yardbirds in 1966, Jimi Hendrix and Cat Stevens 1967, Led Zeppelin in 1973, Queen in 1974, 1975 and 1977, The Police in 1979 and 1982, Rush in February 1978, Iron Maiden in 1980, 1981, and 1983, Status Quo, Kate Bush in 1979, AC/DC's last concert with Bon Scott in January 1980, and Ozzy Osbourne in October 1980. On the afternoon of their 1981 concert there, Slade filmed a music video for their single "Wheels Ain't Coming Down" at the theatre.

The building was still, however, mainly used as a cinema, which was in decline, due to the rise of television. This led to Rank investigating a change of use to, either dance hall or ten-pin bowling alley. This did not happen and many other acts appeared, until the end of the 1980s, when acts preferred larger concert halls and arenas.

The theatre was threatened, with a change of use, again, in 1970, when an application was made to convert it into a bingo hall. This also did not happen, but the owners were still not making money. In 1982, the Rank, again, applied to Southampton City Council, for a change of licence, to turn the building into a bingo hall. This was refused in 1983, the year the building also achieved grade II listed status. The council instead offered to buy the building, for £650,000 and a refurbishment of £3 million. This led to the 1989 setting up of a charitable trust, with the lease for a peppercorn rent, to stop the theatre from becoming a political tool.

The theatre closed for major redevelopment in January 1986, with the entire stage area being improved and additional facilities, such as computerised box office, being added. The theatre opened, as The Mayflower, on 24 February 1987, with a production of Peter Pan starring Bonnie Langford, with the official opening gala, televised in May. Initial audiences proved disappointing and there was talk of the project being a white elephant. This changed, with the introduction of major pantomimes. These attracted huge audiences, peaking with 1994's Dick Whittington, starring Lesley Joseph and John Nettles, which attracted 126,256 theatregoers.