The influences of slight amount of B element on the microstructure and properties of AlCoCrFeNiBx high entropy alloys（x = 0,0.01,…,0.09 and 0.1,mole fraction） were investigated.The AlCoCrFeNi high entropy alloy exhibits equiaxed grain structures with obvious composition segregation.However,with the addition of B element,the alloys exhibit dendrite structures.Inside the dendrites,spinodal decomposition structure can be clearly observed.With the addition of B element,the crystal structures change from（B2 ＋ BCC） to（B2 ＋ BCC ＋ FCC） structures,and the hardness firstly increases from HV 486.7 to HV 502.4,then declines to HV 460.7（x ≥ 0.02）.The compressive fracture strength firstly shows a trend of increasing,and then declining（x ≥ 0.08）.The coercive forces and the specific saturation magnetizations of the alloys decrease as B addition contents increase,the decreasing coercive forces show a better soft magnetic behavior.
