The characterization and magnetic properties of YFe 12− x Mo x ( x=2.0, 2.5 and 3.0) with the ThMn 12-type structure, and the magnetocaloric effect of YFe 9.5Mo 2.5 were investigated. A directional growth was observed in YFe 10Mo 2 alloy. A broad peak in the zero-field-cooling (ZFC) magnetization curve of the YFe 12− x Mo x compounds is ascribed to the existence of ferromagnetic clusters with different site moments and scattered orientations of the moments. The broad range of the peak is reduced with increasing Mo content. A weak peak is observed near 190 K in the ZFC curve of YFe 9Mo 3, which is associated with the 8i sites being mostly occupied by Mo atoms. YFe 9.5Mo 2.5 has a magnetic entropy change of −1.09 J/kg K for a field change of 5 T at 277 K.