A structure of wadded-up seat trim cover, having a plurality of trim cover pieces sewn together at one end, each composed of a wadding member and a skin member, includes a bonded portion formed by bonding the skin member to the wadding member made shorter than the skin member, at a position remote, by a prescribed distance, from the end of the wadding member overlapping the skin member; a first sewn portion formed by bending that portion of the skin member, not overlapping the wadding member, along the end of the wadding member and then by sewing the portions of the adjacent skin members together; and second sewn portions formed by bending each end of the adjacent skin member to the back of the trim cover piece at the first sewn portion and then by sewing the adjacent skin members together at overlapping portions.