A water ball structure includes a base defining a cylindrical housing to received therein a music box type driving device and support thereon a water ball. The driving device is fixed on a disk which is received within a bottom opening of the housing and snap-held by resilient paws formed on the housing. A circumferential wall is provided to fix to and concentrically surround the housing. A rotation ring is supported on the circumferential wall by a ball bearing arranged on the top of the wall so as to allow the rotation ring to be rotatable relative to the housing in a concentric manner by being driven by the driving device through a gear train coupling therebetween. A toothed ring is fit over the housing and snap-held by paws provided on the housing. A number of motion generation devices are provided on the rotation ring, each having a first gear rotatably supported by an output shaft on the rotation ring and a second gear mating between the first gear and the toothed ring so that when the rotation ring rotates about the cylindrical housing, the output shaft of the first gear generates a rotation output through the engagement of the second gear with the toothed ring. A ball support collar is fit into the housing and snap-held by paws formed on the housing to support the water ball.