EN
Magnetic field dependence of critical current density (J_{c}) of bulk MgB₂ material at 20 K is reported. The selected sintered MgB₂ materials contained various amounts of silver. The silver added samples possess always a higher critical current density than the silver free ones. The critical current density increased with silver content and continuously decreased with increase of magnetic field. Further, the normalized volume pinning force density, f_{p}=F_{p}/F_{p,max}, versus reduced field h = H_{a}/H_{irr} for silver free and silver added samples suggested that grain boundary pinning is dominant. In essence, the model of thermal activated flux motion was successfully applied to fit the critical current density of the MgB₂ materials.