A swimming exerciser includes a pair of height adjusting devices each having a base for secure engagement with a pool side and a pole mounted on the base and provided with a slot and multiple cutouts defined in the pole to communicate with the slot. A pair of resilient devices each has a positioning block, a head extending from a side of the positioning block to be movably received in a corresponding one of the cutouts and an elastic strap oppositely formed relative to the head and having a hook. A trapping device has a loop and two opposed rings on the loop to correspond to the two hooks of the two resilient devices. After a swimmer's waist is received in the loop, the swimmer is able to swim in a supported manner in the pool.