Otmoor or Ot Moor is an area of wetland and wet grassland in Oxfordshire, England, located halfway between Oxford and Bicester.

It is encircled by the "Seven Towns" of Otmoor: Beckley, Noke, Oddington, Charlton-on-Otmoor, Fencott, Murcott and Horton-cum-Studley.

Bisected north–south by the Roman Road between Alchester and Dorchester-on-Thames, its name is derived from the Old English for "Otta's Fen".

Watered by the River Ray, it was until the early 19th century unenclosed marshland, and regularly flooded in winter.

Opposition to the motorway was led by Friends of the Earth and included the "Alice's Meadow" campaign.