The origin of the aging of SmCo5magnets is shown to be the reaction with adsorbed air. This reaction can be avoided by excluding all oxygen during the preparation. It is shown that by deformation pressing, nonaging magnets can be made because they are dense enough to avoid oxygen penetration. The adsorbed oxygen reacts with Sm during sintering which results in the formation of undesirable Sm2O3. The formation of these oxides can also be avoided by preparing the samples in oxygen-free atmospheres. During deformation pressing theIHcof the powder decreases considerably; this problem can be solved by using hydrogen-ground powder which has a very high coercive force.