Abstract: A gas-air mixer for internal combustion engines having an inlet and an outlet diffusor and being mounted in a collar member which forms a cyclindrical surface between them. Feeding channels are disposed between the inlet and outlet diffusors which terminate at the external side of the diffusors in a concentrically shaped annular channel. Both diffusors are constructed as separate bushings. The outlet diffusor is fixedly mounted in the collar and the inlet diffusor is movably mounted in the collar, around its axis by means of a control lever. The diffusors are seated end face to end face and an outer cylindrical surface mutually defined by them through which have been cut radial slots form feeding channels for gas fuel. By turning of said diffusors with respect to each other the cross-section of the feeding channels is adjusted depending on the angle of rotation of the inlet diffusor around its axis different operating regimes of the engine.