Abstract: A chair has a coupling mechanism between a seat and a back, which includes a joining member, and a coupling member; the seat has two opposite front and two opposite rear ears on a bottom; the joining member is secured on a supporting tube for the seat, and has two opposite sloping slots on each end, and intermediate adjustment slots; the connecting member has a front fixing hole, and a rear sloping slot; the joining member, the connecting member, and the seat are joined together with a first shaft passed through the front ears and the front sloping slots, with a second shaft passed through the rear ears and all of the rear sloping slots; a third shaft is passed through the adjustment slots and the fixing hole; the connecting member is further pivoted to the joining member at a middle portion; the back is joined to the connecting member.