A connector for medical lines includes a tubular body having a male luer-lock fitting at one end, intended to be screw-coupled with a complementary female fitting. An outer jacket is coupled in unidirectional rotation with the tubular body in the direction corresponding to the screwing of the male fitting and freely rotatable in the opposite direction. For selectively coupling the outer jacket with the tubular body in the direction corresponding to the unscrewing of the male fitting, at least one side push-button carried by said outer jacket is provided.