A pistol frame is suitable for mounting of a trigger mechanism which includes a trigger mechanism housing having a through channel. The pistol frame includes an upper frame portion defining a rear receiving space, and a rear rail block disposed in the rear receiving space and including a bottom plate, and two side plates extending upwardly the bottom plate. Each side plate has a through hole suitable for aligning with the through channel to permit extension of a trigger housing pin therethrough to thereby fix the rear rail block and the trigger mechanism housing to the upper frame portion. The bottom plate and the side plates cooperatively define at least one receiving space suitable for receiving the extensions.