A homokinetic universal joint having an outer ring formed in its inner surface with three axial track grooves, a tripod member inserted in the outer ring and having three legs, and guide blocks pivotally and axially slidably mounted on the respective legs and received in the respective track grooves. The guide blocks are formed in each side thereof with a ball circulating passage having straight raceways. A plurality of balls are rollingly received in each ball circulating passage. The track grooves are formed at both sides thereof with raceway grooves extending parallel to the axis of the track grooves to guide the balls along the straight raceways.