An oil cooler for a vehicle includes an inflow tank through which a working fluid flows in. An outflow tank is spaced apart from the inflow tank by a predetermined interval and has a discharge hole at one side which faces the inflow tank. A plurality of tubes connect the inflow tank with the outflow tank longitudinally such that the working fluid flows therethrough. A bypass valve is integrally mounted at an outer side of the one end portion of the inflow tank and connected to an inner side of the inflow tank to bypass or flow the working fluid flowed therein into the inflow tank by selectively opening and closing according to a temperature of the working fluid. An outflow pipe has one end mounted to the discharge hole and another end thereof mounted to the bypass valve to connect the outflow tank with the bypass valve.