A diminishable and distensible ball net bag structure includes a net bag bottom portion, a net bag mouth rim portion, a net bag peripheral side which adjoins the net bag bottom portion and the net bag mouth rim portion, and at least four resilient elements spaced apart and disposed at four portions or at the four portions and junctions of every two adjacent said portions of the net bag peripheral side, respectively. Hence, a ball net bag for holding balls is formed. In the case of a few balls, the resilient elements contract while keeping the balls close to a mouth of the ball net bag. In the case of plenty balls, the resilient elements not only stretch and thus distend the ball net bag but also keep the balls close to the mouth to ensure easy access thereto even when the balls are removed from the ball net bag one by one.