Abstract: An improved butterfly valve for intercepting a conduit where substances flow, especially suitable for the pharmaceutical, alimentary and chemical fields The valve comprises an annular body (1) integral with the conduit and acting as a support for the rotation stem (4) of the butterfly valve dish (3), which is operable at one end by an actuating lever (6) to open or close the internal port of the annular body (1) where a sealing member (2), tightly engaging with the butterfly valve dish (3) in the closed position, is housed. The body (1) comprises means for allowing an extremely quick and easy mounting and dismounting operations for cleaning purposes without affecting the sealing ability, operability and minimum flow resistance when the valve is fully open. The sealing member (2) is shaped to require a low effort while closing the valve as well as assuring the seal even in correspondence of the stem (4) of the butterfly valve dish (3).