A hydraulic control system for a four-wheel drive torque transfer mechanism for a vehicle, including an automatic transmission, a transfer mechanism having gear positions of a two-wheel drive direct-coupling mode H.sub.2, a four-wheel drive direct-coupling mode H.sub.4 and a reduced-speed four-wheel drive mode L.sub.4, and a hydraulic control circuit for controlling the transmission and the transfer mechanism. The transfer mechanism includes a reduction gear mechanism, a first output shaft, a second output shaft rotationally connectible to the first output shaft through a link mechanism, a four-wheel drive clutch for releasably coupling the first and second output shafts, a direct-coupling clutch for releasably coupling an input shaft of the reduction gear mechanism with the first output shaft, and a reduction brake for setting the reducing gear mechanism in a gear train of the reduced-speed mode. The hydraulic control circuit includes an inhibitor valve which is supplied with governor pressure and which selectively applies pressurized fluid to one of the servomotors of the direct-coupling clutch and reduction brake while draining the other servomotor, the inhibitor valve feeding pressurized fluid continuedly to the servomotor of the direct-coupling clutch if manual shift of the transfer mechanism selects the mode L.sub.4 when the governor pressure is higher than a predetermined level, and instead feeding pressurized fluid to the servomotor of the reduction brake and draining the servomotor of the direct-coupling clutch when the governor pressure drops below the predetermined level.