A joint rotary axis positioning unit of ankle rehabilitation device is disclosed, including: a shoe body provided therein inner and outer positioning discs, inner and outer rotary pieces for matching the inner and outer positioning discs, and first, second, third and fourth flexible pieces. The inner rotary piece includes first and second circular sheet bodies with a plurality of first front and first rear through holes. The outer rotary piece has third and fourth circular sheet bodies with a plurality of second front and second rear through holes. A first front inserting pin of the first flexible piece penetrates the first through holes of the first and second circular sheet bodies and is limited by the inner positioning disc. A first rear inserting pin of the second flexible piece penetrates the second through holes of the first and second circular sheet bodies and is limited by the inner positioning disc. A second front inserting pin of the third flexible piece penetrates the second through holes of the third and fourth circular sheet bodies and is limited by the outer positioning disc. A second rear inserting pin of the fourth flexible piece penetrates the second through holes of the third and fourth circular sheet bodies and is limited by the outer positioning disc. A first penetrating axis is pivotally connected to the first and second flexible pieces, the first circular sheet body, the inner positioning disc and the second circular sheet body. A second penetrating axis is pivotally connected to a third slotted hole of the third flexible piece, a fourth slotted hole of the fourth flexible piece, the third circular sheet body, the outer positioning disc and the fourth circular sheet body. The first penetrating axis is higher than the second penetrating axis so as to enable the turning angle between the inner and the outer rotary pieces to be close to a moving angle of the ankle, thereby helping a wearer to walk smoothly and preventing the wearer from stumble.一種
