The (Fe0.5Co0.5)71-xNbxZr3Nd4B22 bulk alloys (x=0-10) were prepared by suction casting into a copper mould. The effects of Nb addition on glass-forming ability (GFA) and magnetic properties of the alloys were investigated. Results show that proper addition of Nb can increase the GFA of the alloy effectively. When the Nb content reached 5at%, a new bulk amorphous alloy, (Fe0.5Co0.5)66Nb5Zr3Nd4B22 with fully amorphous structure was obtained. The amorphous alloy exhibits typical soft magnetic property, and the saturation magnetization (Ms) is 79 Am2/kg. Its crystallization temperature (Tx) and crystallization activation energy of the alloy are 957 K and 538.30 kJ/mol, respectively.