Machine for sealing plastic profiled elements, comprising: - at least a base frame; - retention means (7, 8) of at least a profiled element of plastic material having a first main face, a second main face, a first lateral face, a second lateral face and respective areas to seal, said retention means (7, 8) being associated with said base frame and comprising at least a first support element movable along a first direction of sliding and at least a second support element mounted on said first support element and movable relative thereto along a second direction of sliding substantially transverse to said first direction of sliding, said main faces (2, 3) being adapted to come into contact with said support elements (7, 8) respectively; - at least a heat-sealing element with heated plate, mounted on said base frame and having two mutually opposite surfaces on which said areas to seal to be heated are placeable in contact; - sliding means (9, 10) of said retention means (7, 8), which are placed between said base frame and said retention means (7, 8) and are adapted to shift said profiled elements between a position of reciprocal moving away and a position of mutual approach wherein said heated areas to seal are joined together; - positioning means (13, 14) associated with said support elements (7, 8) and adapted to receive and support at least a portion of at least one of said lateral faces (4, 5); characterized by the fact that it comprises: - locking means (15, 28) movably associated with said retention means (7, 8) and adapted to keep said profiled elements in a locking configuration wherein at least one of said main faces (2, 3) is kept into contact with at least one of said support elements (7, 8) and at least one of said lateral faces (4, 5) is arranged into contact with said positioning means (13, 14), in said locking configuration said locking means (15, 28) being adapted to prevent said profiled elements from rotating around the longitudinal axis of the profiled elements themselves. - at least a base frame; - retention means (7, 8) of at least a profiled element of plastic material having a first main face, a second main face, a first lateral face, a second lateral face and respective areas to seal, said retention means (7, 8) being associated with said base frame and comprising at least a first support element movable along a first direction of sliding and at least a second support element mounted on said first support element and movable relative thereto along a second direction of sliding substantially transverse to said first direction of sliding, said main faces (2, 3) being adapted to come into contact with said support elements (7, 8) respectively; - at least a heat-sealing element with heated plate, mounted on said base frame and having two mutually opposite surfaces on which said areas to seal to be heated are placeable in contact; - sliding means (9, 10) of said retention means (7, 8), which are placed between said base frame and said retention means (7, 8) and are adapted to shift said profiled elements between a position of reciprocal moving away and a position of mutual approach wherein said heated areas to seal are joined together; - positioning means (13, 14) associated with said support elements (7, 8) and adapted to receive and support at least a portion of at least one of said lateral faces (4, 5); characterized by the fact that it comprises: - locking means (15, 28) movably associated with said retention means (7, 8) and adapted to keep said profiled elements in a locking configuration wherein at least one of said main faces (2, 3) is kept into contact with at least one of said support elements (7, 8) and at least one of said lateral faces (4, 5) is arranged into contact with said positioning means (13, 14), in said locking configuration said locking means (15, 28) being adapted to prevent said profiled elements from rotating around the longitudinal axis of the profiled elements themselves.