A hydraulic control system comprises first and second shift valves which cooperate with each other to effect a shift between two gear ratios. The first shift valve has a port and two different pressure acting areas which are exposed to pressure from the port depending upon downshift and upshift states of the first shift valve, respectively. The second shift valve effects communication between signal pressure generating means and the port of the first shift valve when the second shift valve is in one of two states to deliver the signal pressure to the port of the first shift valve.