Cirencester Grammar School was an historic school in Cirencester, Gloucestershire, United Kingdom.

The school had a history of over 500 years before it closed in July 1966 as part of a government reorganisation in education. In September 1966 it became part of Cirencester School (combining with the Deer Park Secondary Modern School) and took no new First Form, who went directly to the Deer Park.

Eventually the old CGS forms moved to the Deer Park altogether. The Victoria Road grammar School site still exists and is now a Junior School, remaining much as it was in 1966. It played an important and distinguished role in the education of the people of Cirencester and the surrounding area.

One of its most famous pupils was Edward Jenner who invented the process of inoculation to control infectious diseases. Another famous pupil was the cricketer, Wally Hammond, whose centenary was celebrated at a reunion in Cirencester on 11 October 2003.