A radially adjustable horse grazing muzzle includes a muzzle body made of a flexible material and having an open end for allowing a horse snout to be placed in the muzzle body therethrough, and an adjustment assembly configured as a segment of a periphery of the open end of the muzzle body and having a pad and at least one adjustable fastener composed a first member and a second member, wherein the first member is fixed to the pad while the second member is fixed to an adjacent segment of the periphery of the open end of the muzzle body, the first and second members being configured to combine with an adjustable overall length thereof, whereby when the overall length of the combined first member and second member is reduced, the muzzle body is centripetally converged, thereby achieving a radial adjustment of the muzzle.