An eccentric butterfly valve comprising a valve body formed therein with an internal flow passage extending in a direction of a flow passage axis, a disk-shaped valve member disposed in the internal flow passage and supported by the valve body through valve stems to be rotatable about a rotation axis perpendicular to the flow passage axis, and a seat ring attached to an inner periphery of the internal flow passage, said seat ring defining a sealing plane sealing the internal flow passage between the seat ring and an outer peripheral edge portion of the valve member in valve closing, said rotation axis being located eccentrically in the direction of the flow passage axis from a sealing surface, wherein the valve stems include a first valve stem and a second valve stem; the valve body is formed therein with a stem through-hole and a stem bottomed-hole, said stem through-hole extending through the valve body from an outer peripheral surface of the valve body to the internal flow passage, said first valve stem being rotatably inserted through the stem through-hole, said stem bottomed-hole rotatably supporting the second valve stem; the valve member is provided with a fitting hole; and the first valve stem extends through the stem through-hole and is provided at a tip portion thereof with a fitting portion, said fitting portion being fitted into the fitting hole, so that the first valve stem is unrotatably coupled to the valve member, and the second valve stem is provided, at a tip portion thereof projecting from the stem bottomed-hole, with an engagement portion, characterized in that the valve member is provided with an engagement groove at a position thereof opposite to the fitting hole in the direction of the rotation axis, wherein the engagement portion of the second valve stem is inserted into the engagement groove in a direction perpendicular to the rotation axis, so that the second valve stem is unrotatably coupled to the valve member. wherein the valve stems include a first valve stem and a second valve stem; the valve body is formed therein with a stem through-hole and a stem bottomed-hole, said stem through-hole extending through the valve body from an outer peripheral surface of the valve body to the internal flow passage, said first valve stem being rotatably inserted through the stem through-hole, said stem bottomed-hole rotatably supporting the second valve stem; the valve member is provided with a fitting hole; and the first valve stem extends through the stem through-hole and is provided at a tip portion thereof with a fitting portion, said fitting portion being fitted into the fitting hole, so that the first valve stem is unrotatably coupled to the valve member, and the second valve stem is provided, at a tip portion thereof projecting from the stem bottomed-hole, with an engagement portion, characterized in that the valve member is provided with an engagement groove at a position thereof opposite to the fitting hole in the direction of the rotation axis, wherein the engagement portion of the second valve stem is inserted into the engagement groove in a direction perpendicular to the rotation axis, so that the second valve stem is unrotatably coupled to the valve member.