Castle Mill is a graduate housing complex of the University of Oxford in Oxford, England.

Castle Mill is located north of Oxford railway station along Roger Dudman Way, just to the west of the railway tracks and the Oxford Down Carriage Sidings, on what was formerly Cripley Meadow, south of Port Meadow. The initial buildings at the southern end of the site were completed in 2004. Accommodation is available for single people, couples, and families. Graduate students with children benefit from priority access to lower-cost accommodation, alleviating the over-stretched housing market in Central Oxford.

Facilities at Castle Mill include a common room, launderettes, bicycle racks and an outside barbecue area. The complex is supported by caretakers who live on site. The proximity of the railway causes a noise issue.

The Castle Mill Stream, a branch of the River Thames, runs to the east of the site beyond the railway tracks, hence the name. From Castle Mill there are views of the railway lines to the East, and allotments and Port Meadow to the West.

In 2010, Oxford City Council capped the number of students that Oxford University and Oxford Brookes University were permitted to have in private rented housing to 3,000 each. The Council was encouraged by local lobbies such as the East Oxford Residents Forum to use planning permission as an enforcement mechanism. If either University breached the cap, the Council threatened to prevent new buildings from being occupied. As a consequence of these restrictions, the Universities looked to develop sites for student accommodation in partnership with commercial providers.

Since 2012, the Oxford University Estates Directorate, with the help of Longcross, have been developing the 2½ acres (one hectare) Castle Mill brown field site, north of the existing accommodation, between the Cripley Meadow Allotments and the railway tracks, close to the southern end of Port Meadow, to meet the need for graduate places.

The development has been controversial, since the four to five storey blocks overlook Port Meadow, an historic open area to the north with views of some of Oxford's skyline. Campaigners warned of damage to views of Oxford. There was an online petition and a "Save Port Meadow" campaign was established in December 2012. Concern was raised by the Oxford Preservation Trust, Layla Moran MP, the Liberal Democrats, and Green Party. Some members of Oxford University expressed anger. The development has been likened by a critic to building a "skyscraper beside Stonehenge".

In February 2013, a local newspaper reported that Oxford City Council had entered negotiations with Oxford University to reduce the height of the buildings by two storeys. There was a protest and picket of Congregation, the University's formal assembly of senior members, at the Sheldonian Theatre in central Oxford. The protesters including members of the University, such as Diarmaid MacCulloch, Professor of the History of the Church and TV historian. Oxford University donors, such as Michael Moritz, and the University's Vice-Chancellor, Prof. Andrew Hamilton, were also targeted with letters by the protesters, warning that the buildings "blot out the unique view of Oxford's Dreaming Spires from Port Meadow". Campaigners claimed that the decision on the development was unlawful. The author Philip Pullman condemned the buildings; this was featured in the national press.