A hydraulic control system for 4-speed automatic transmissions in which line pressure, drive pressure, reverse pressure and low pressure are selectively supplied from a manual valve to an underdrive clutch, an overdrive clutch, a low-reverse brake, a reverse clutch, and a second brake to realize four forward speeds and a reverse speed. The hydraulic control system includes an underdrive pressure control valve provided between a drive pressure line and the underdrive clutch, and controlled by a first solenoid valve; an overdrive pressure control valve provided between the drive pressure line and the overdrive clutch, and controlled by a second solenoid valve; a second/low-reverse pressure control valve connected to a line pressure line and controlled by a third solenoid valve; a solenoid switch valve controlled by low pressure, line pressure or drive pressure supplied respectively from a low pressure line, the line pressure line and the drive pressure line, and which supplies hydraulic pressure to the low-reverse brake and the second brake; and a fail-safe valve provided between the solenoid switch valve and the second/low-reverse pressure control valve, and is controlled by operational pressure of the underdrive clutch and overdrive clutch, line pressure, and drive or reverse pressure, the fail-safe valve preventing hydraulic pressure supplied from the second/low-reverse pressure control valve from being simultaneously supplied to the second brake and the low reverse brake. The reverse clutch is directly communicated with the manual valve via a reverse pressure line.