A joint angle adjustment mechanism is provided. A base has a center and two side boards opposite to each other, and at least one of the two side boards has toothed recesses arranged curvedly and open toward the center. Two connecting members are respectively connected to the base, and at least one of the two connecting members is pivoted to the base. At least one adjustment mechanism is axially pivoted to the base about the center, each said adjustment mechanism includes a positioning assembly including a slidable seat, a positioning member and an elastic member within the slidable seat, the positioning member is slidably arranged within the slidable seat and optionally moves radially to be engaged with or disengaged from one of the toothed recesses, the elastic member radially urges the positioning member to engage with one of the toothed recesses.