The authors studied the influence of microstructure and grain size, as well as Curie temperature, on the low-temperature aged Sm(Co0.45Cu0.4Fe0.15)5 alloy in relation to enhanced coercivity. Melt-spinning has been employed in order to achieved a wide range of grain sizes from micro- to nanometer level. XRD and TEM analysis were used to study the structure of as-spun ribbons and SQUID magnetometer was used to determine the magnetic hysteresis parameters. Results showed that the enhanced coercivity of aged ribbons is higher than that one obtained in 1:5 microstructure aged magnets prior to the changes in Curie temperature.