A hydraulic control system for an automatic transmission has an inhibitor valve which comprises a change-over valve having a first set position and a second set position and functioning to supply and discharge a hydraulic pressure to and from a hydraulic servomechanism for a friction engaging element through its movement between the first and second set positions; an arrangement for urging the change-over valve to the first set position; a plunger having a first set position and a second set position and functioning to bring the change-over valve into the second set position when the plunger is urged to the second set position. The inhibitor have functions to perform the supply and discharge of the hydraulic pressure to and from the hydraulic servomechanism in accordance with a first hydraulic signal and a second hydraulic signal through an arrangement which produces the first hydraulic signal for urging the change-over valve to the second set position and urging the plunger to the first set position. An arrangement produces the second hydraulic signal for urging the plunger to the second position; and an arrangement delays a discharge of the second hydraulic signal.