Provided is a check valve installed in a bore of a modulator block having an inlet path and an outlet path to control a flow of oil in one direction, the check valve including: a valve housing provided with a path hole passing through at a central portion thereof to have an upper end and a lower end thereof open to communicate with the inlet path and the outlet path, and a flange portion protruding from a circumference of an outer surface of the valve housing such that the valve housing is fixed to the bore; a spring retainer coupled to one of the open upper and lower ends of the valve housing which is adjacent to the outlet path, and having an outlet port communicating with the outlet path; a plunger movably installed in the path hole while being elastically supported by a spring supported on the spring retainer, and configured to open or close the path hole according to an up and down movement of the plunger; and a lip seal having a lip portion interposed between the plunger and the valve housing to prevent oil from flowing backward toward the inlet path from the outlet path.