Disclosed herein are a sealing member for a master cylinder and a master cylinder having the same. The master cylinder is configured such that a communication hole of a piston is rapidly brought into communication with an oil path toward an oil tank upon release of braking. This may minimize meaningless retracting movement of the piston and delay in a braking release operation. The sealing member for the master cylinder includes an outer wing part to come into contact with the cylinder body, and an inner wing part to come into contact with the outer surface of the piston. The inner wing part includes a seal formed at a tip end thereof and at least one oil passage formed in a surface thereof opposite the outer surface of the piston