Provided are an exhaust duct, an exhaust duct assembly, and an aircraft using the exhaust duct. The exhaust duct has a structure that enables combustion gas to be diverged and discharged from an inlet end to a first outlet end and a second outlet end at respective sides of the exhaust duct. The exhaust duct includes a first housing including a first body forming an outer wall of the inlet end, and further includes second bodies respectively extending on respective sides from the first body and respectively forming the first outlet end and the second outlet end; a second housing spaced apart from the first body, forming an inner wall of the inlet end, and extending curvedly toward the second bodies; and a connection housing connecting the first housing to the second housing and including at least one recess portion recessed toward the inlet end.