A folding ball trolley having minimized volume has a frame, a bag and multiple resilient elements. The frame has four stand rods, four top seats, four sliding seats, four wheels, four connecting rod assemblies and four mounting rods. The bag connects to the mounting rods and the mounting rods pivotally connect to the stand rods. Accordingly, the mounting rods can be rotated relative to the stand rods such that the mounting rods do not protrude upward to occupy too much space when the ball trolley is folded. Besides, the frame is braced by the resilient elements so a user does not have to stretch his hands between the rods when folding the ball trolley, thereby preventing the hands from being clamped.