Abstract: A small pipe fitting in which a male body and a female body cannot be separated after they are coupled once. The pipe fitting (10) consists of a male body (12), and a female body (30) into which the male body (12) is inserted. The male body (12) has a smaller outside diameter on the distal end side and includes, sequentially from the distal end, a third cylindrical portion (14), an outer tapered portion (16), a second cylindrical portion (18), an annular groove (20) locked with a resilient stop ring body (42), and a first cylindrical portion (22). The female body (30) has a smaller inside diameter on the rear side and includes, sequentially from the distal end and from the inlet side of an opening (32), a first inner wall face (34), a two-step groove (40) consisting of a locking groove (36) and a containing groove (38) and containing the resilient stop ring body (42), a second inner wall face (44), an inner tapered portion (46), and a third inner wall face (48).