This paper proposes an obstacle avoidance technique for small size drones by using a monocular camera. This method can assist the drone for doing their mission and avoid hitting any obstacle or minimise the collision as possible. For avoiding an obstacle while the drone is doing its mission, We use a computer vision technique to determines the free zone along with the obstacle that may cause a crash and send feedback control to the drone. The small size drone receives feedback about the obstacle and commands the drone to moves to a safe area then resume its trajectory.