A grip (10) of a firearm (12), particularly of a gun, comprises a body (14) extending substantially in a development direction (16) and a gripping portion (20) removably mounted on the body (14) in a rear area with reference to a trigger of the weapon. The gripping portion (20) at least partially envelops and covers a rear surface (14a) and a tract of side surfaces (14b) of the body (14). Means for locking the gripping portion (20) on the body (14) operating in an inserting direction (24) transversal to the development direction (16) are arranged in at least one side portion of the body (14) and the gripping portion (20) and comprise first strikes (52) associated with the gripping portion (20) and offset in the development direction (16) relative to second strikes (54) associated with the body. Interference means are interposed between the first and second strikes (52, 54) for locking the gripping portion (20).