This paper describes the effect of small amount of copper addition on the magnetic properties of deformation-aged Cr-Co-Fe alloys. The addition of Cu makes the early stage of demagnetization extremely difficult, and in some cases, very little demagnetization is seen up to demagnetization fields of several hundred oersteds. The deformation-aged Cr-Co-Cu-Fe alloys exhibit higher Br/Bs (>0.99), Hc, and (BH)max values than the ternary Cr-Co-Fe alloys. In the case of magnetic field heat treatment, however, the Cu addition did not give any improvement in magnetic properties. The permanent magnet properties of the Cr-Co-Cu-Fe alloys with various cobalt contents have been studied. The energy products increase by 0.5 ∼ 1 MGOe when 2 wt% Cu is added to the ternary alloys. Consequently, the Cu-addition serves as a partial substitution for cobalt which is an expensive as well as strategic element. The deformation-aged Cr-Co-Cu-Fe alloys yield a (BH)max value of ∼ 8 MGOe at 16 wt% cobalt, and ∼ 10 MGOe at 23 wt% cobalt. The latter is the highest energy product ever reported in Cr-Co-Fe base alloys.