A one-way valve (6) for medical infusion lines and the like, comprising a first tubular element (2) and a second tubular element (3), which define, respectively, an upstream duct (4) and a downstream duct below (5), which are coaxial with each other and fixed transversely between which is a diaphragm (8) made of deformable elastic material that cooperates in a narrow fluid path with an annular valve seat (12) of said first tubular element (2) ) to keep said valve (6) normally closed, in which a predetermined fluid pressure in said upstream conduit (4) causes an elastic displacement or deformation of said diaphragm (8) and the consequent opening of said valve (6), and wherein said annular valve seat is defined by a wall with conical surface (12) of said first tubular element (2) which is divided towards said second tubular element (3), and said diaphragm constitutes by the end wall (8) of a cup-shaped element (7), the outer peripheral edge (8a) of which is normally pressed in sealed contact against said annular valve seat (12), under an axial thrust exerted by the side wall (9) of said cup-shaped element (7), the deflection or axial displacement of said end wall (8) of the cup-shaped element (7) causes a predetermined fluid pressure during use, determining the radial contraction of said outer peripheral edge (8a) and its consequent separation from said annular valve seat (12), and in which said side wall (9) of the cup-shaped element (7) has its free edge (9a) resting against a cross-sectional surface (14) of said second tubular element (3) that communicates with said downstream conduit (5) and that has an arrangement of radial channels (15), said valve characterized in that said radial channels (15) of said surface striated transverse (14) they are separated by alternately elevated (17) and sunken (18) sectors that define angular rest portions (17) angularly separated by non-resting angular portions (18), said free edge (9a) of the side wall (9) of said cup-shaped e
