Heavy rare earth substitution for Sm in SmCo5magnets were carried out with a view of improving the reversible temperature coefficient (RTC) of magnetization. The RTC was found to vary depending on the temperature ranges of interest. Over the range of −50 C to +100 C for Sm0.6Dy0.4Co5and Sm0.68Er0.08Ho0.08Dy0.08Gd0.08Co5an RTC of +0.0062&percent; per °C and −0.0045&percent; per °C respectively was obtained with a (BH)maxexceeding 11 MGOe.