This paper presents the altitude control of a quadrotor system under the disturbance. The altitude is measured by an ultra sonic sensor attached at the bottom of the quadrotor system and the measured altitude data are used in the time-delayed controller. To test the robustness of the controller, a weight attached to the center of the system is dropped intentionally several times to cause disturbances to the system. Performances of the altitude control by the PID control and time-delayed control method are compared experimentally. Experimental studies are conducted to verify the outperformance of the time-delayed controller for controlling the altitude of the quadrotor system under disturbances.