A series of the Gd5.1Si2Ge2-xBx alloys were prepared with arc melting in purified argon atmosphere.The effect of B addition on the magnetocaloric effect of compound Gd5Si2Ge2 was investigated by powder X-ray diffraction technology and DSC and direct magnetocaloric effect apparatus and vibrating sample magnetometer (VSM).The results show that the addition of a small amount of B maintains the Gd5Si2Ge2 compound in single monoclinic phase with superior magnetocaloric effect,especially when x=0.01,the maximum magnetic entropy change (|ΔSM|) reaches the values of 13.7 J/(kg·K) at 288 K in 1.5 T magnetic field.With the increase of B content,some orthorhombic Gd5Si4-type phases appear in the matrix of monoclinic Gd5Si2Ge2-type phase in Gd5.1 Si2-xGe2Bx alloys.