[en] This paper reports on superconducting coupling nature at grain boundaries in Bi₂Sr₂CaCu₂O_x glass-ceramics which consist mainly of the low-T_c phase first examined by measuring superconducting properties and temperature or ac field dependence of ac complex susceptibility. It was found from the ac loss peaks that superconducting coupling at grain boundaries was basically characterized by three types of weak links. The weak-link behaviors at grain boundaries depended strongly on cooling conditions after annealing and annealing time and temperature. Particularly, it was found that the weak links at grain boundaries were improved by prolonged annealing at 840 degrees C. The furnace-cooled glass-ceramics obtained by annealing at 820 degrees or 840 degrees C for about 200 h exhibited a critical transport current density (77 K, zero magnetic field) of about 200 A/cm²