A traveling control system for a hydraulically driven vehicle enables the vehicle to travel at a higher speed and also enables a vehicle body to be braked appropriately when the vehicle descends a slope with a travel control valve kept in its neutral position. The traveling control system includes pressure switches for detecting an operative state of a travel control valve, a detection line for detecting a shift position of a transmission, and a controller, a solenoid valve, load lines, a shuttle valve and a control line for cooperatively increasing the capacity of a travel motor upon the detection of that the travel control valve is in its neutral position and also the transmission is shifted to a high-speed gear. A timer function of the controller allows the capacity of the travel motor to be increased after the elapse of a predetermined time after the detection of that the travel control valve is in the neutral position. The load lines and the shuttle valve jointly serve as a hydraulic source for switching the motor capacity.