Although the facility at Shipton-on-Cherwell, near Kidlington will remain open as a valuations and consignment office, the last auction there will be a vernacular furniture and works of art sale on September 30.
Following the closure of other regional outposts in Knowle (2011) and Chester (2013), Bonhams now conduct sales in the UK from three rooms: Edinburgh, Knightsbridge and New Bond Street.
Bonhams' press officer Andrew Currie said: "We've taken this decision because most of our UK regional revenue now comes from transferring items to our international salerooms in London and elsewhere. It makes sense for the Oxford team to concentrate on this increasingly important part of Bonhams' business."
The specialist Oak Interior sales conducted at Oxford will move to New Bond Street and items of sporting memorabilia to Edinburgh but the toys and dolls department is now closed. Bonhams say nine of the 26 Oxford employees will remain with the company, including oak and vernacular specialist David Houlston.
Based in Oxford city centre for many years, Bonhams developed a former Mercedes showroom on the Banbury Road into a spacious modern auction building in 2008 to host collectors' car and motorcycle sales as well as auctions across the spectrum of disciplines from antiquarian books to modern art.
More business moved to Oxford with the closure of Bonhams Chester in 2013 when the auction calendar grew to approximately 45 sales a year.