A hinge for an orthopedic brace including: a pivot shaft; a lower leg plate pivoted to said pivot shaft; an upper leg plate; a catch plate (22A, 22B) secured to an end portion of said upper leg plate and having an annular portion that is sleeved around said pivot shaft and that has a toothed peripheral edge; and two position adjusting units (9A, 9B) mounted rotatably on said catch plate (22A, 22B), said hinge being characterized in that each of said position adjusting units (9A, 9B) includes a rotatable limiting seat, a limiting pin, and a slider body, said rotatable limiting seat having a seat housing that defines a housing chamber therein and that is formed with a wall slot which extends in a radial direction with respect to said pivot shaft, said slider body being slidably disposed in said housing chamber and being slidable relative to said seat housing in the radial direction between engaging and disengaging positions, said limiting pin extending outwardly of said housing chamber from said slider body through said wall slot so as to be co-slidable with said slider body relative to said seat housing; said limitingpin of each of said position adjusting units (9A, 9B) engaging said toothed peripheral edge when said slider body is disposed at the engaging position, thereby preventing rotation of said position adjusting unit (9A, 9B) relative to said catch plate (22A, 22B) about said pivot shaft, and being disengaged from said toothed peripheral edge when said slider body is disposed at the disengaging position, thereby permitting rotation of said position adjusting unit (9A, 9B) about said pivot shaft; and said annular portion of said catch plate (22A, 22B) being formed with two circumferentially extending guiding grooves (224A, 224B), said rotatable limiting seat of each of said position adjusting units (9A, 9B) further having a tongue (917A, 917B) that protrudes from said seat housing into a respective one of said circumferentially extending guiding grooves (224A, 224B), so that rotation of each of said rotatable limiting seats about said pivot shaft is guided along the respective one of said circumferentially extending guiding grooves (224A, 224B). a pivot shaft; a lower leg plate pivoted to said pivot shaft; an upper leg plate; a catch plate (22A, 22B) secured to an end portion of said upper leg plate and having an annular portion that is sleeved around said pivot shaft and that has a toothed peripheral edge; and two position adjusting units (9A, 9B) mounted rotatably on said catch plate (22A, 22B), said hinge being characterized in that each of said position adjusting units (9A, 9B) includes a rotatable limiting seat, a limiting pin, and a slider body, said rotatable limiting seat having a seat housing that defines a housing chamber therein and that is formed with a wall slot which extends in a radial direction with respect to said pivot shaft, said slider body being slidably disposed in said housing chamber and being slidable relative to said seat housing in the radial direction between engaging and disengaging positions, said limiting pin extending outwardly of said housing chamber from said slider body through said wall slot so as to be co-slidable with said slider body relative to said seat housing; said limitingpin of each of said position adjusting units (9A, 9B) engaging said toothed peripheral edge when said slider body is disposed at the engaging position, thereby preventing rotation of said position adjusting unit (9A, 9B) relative to said catch plate (22A, 22B) about said pivot shaft, and being disengaged from said toothed peripheral edge when said slider body is disposed at the disengaging position, thereby permitting rotation of said position adjusting unit (9A, 9B) about said pivot shaft; and said annular portion of said catch plate (22A, 22B) being formed with two circumferentially extending guiding grooves (224A, 224B), said rotatable limiting seat of each of said position adjusting units (9A, 9B) further having a tongue (917A, 917B) that protrudes from said seat housing into a respective one of said circumferentially extending guiding grooves (224A, 224B), so that rotation of each of said rotatable limiting seats about said pivot shaft is guided along the respective one of said circumferentially extending guiding grooves (224A, 224B).