A folding knife capable of preventing automatic folding, which includes a handle having first, second and third plates, and a blade pivotally connected between the first and second plates by a pivot. The second plate is provided with a resilient stopper having a first end fixed to the second plate and a second end extending toward the first plate in a slanting manner. The third plate has one side corresponding in position to the second plate and concavely provided with an engaging hole. When the blade is fully rotated out of the handle, the second end of the resilient stopper presses against one end of the blade and thereby keeps the blade fully rotated out of the handle. Thus, when a force applied to the blade is excessively large, the resilient stopper will not be shifted away from the position against the blade.