The Knavesmire is one of a number of large, marshy undeveloped areas within the city of York in North Yorkshire, England, which are collectively known as Strays. Knavesmire, together with Hob Moor, comprises Micklegate Stray. The York Tyburn, the site of a gallows administered on behalf of The Crown by York Castle, was situated in the area adjacent to the Tadcaster Road.

It has been suggested that the name 'Knavesmire' may share a derivation with Knaresborough—Cenward's mire.

Situated in the south-west of the city, some distance outside the historic walls, Knavesmire's low-lying position makes it liable to severe flooding in times of heavy rain. As a consequence, it remained undeveloped as the city expanded around it.

The Knavesmire was the site of York Golf course for many years.

During the Second World War, parts of the Knavesmire were farmed, while other parts were used for military purposes including an anti-aircraft battery and a prisoner of war transit camp which was located near the grandstand.

Knavesmire was also the site of Knavesmire Secondary School, which then became one of the campuses of The College of Law till 2014. Millthorpe School uses the Knavesmire for cross country running. Knavesmire Primary School is located on Campleshon Road, at the southern end of Knavesmire Road. In 1864 a letter was sent to the York press from H. J. Jenkinson of the Leeds football club suggesting that the citizens of York form a football team and that they should play a friendly match on Knavesmire.

Between 2009 and 2022, it was also home to Yorkshire's largest beer festival. The annual York CAMRA Beer & Cider Festival was held in a marquee on Knavesmire opposite the Grandstand.

For many years, Knavesmire was the site of public hangings in York. The gallows were erected in 1379, a few miles outside the city on the main southern approach road (now known as the A1036 Tadcaster Road). The execution site was often referred to as "York Tyburn" after the original Tyburn gallows in Middlesex.