The high-temperature magnetic properties of precipitation-hardened Gd x Co 8 9 . 5 - x - y Fe 8 Cu y Zr 2 . 5 (x=11.5-13.5 and y=7-17) alloys have been studied systematically. X-ray diffraction and transmission electron microscopy reveal that a cellular microstructure consisting of 2:17 cells surrounded by 1:5 cell boundaries is obtained after precipitation hardening. Thermomagnetic analysis further confirms the two-phase character and indicates that Cu mainly goes into the 1:5 phase. All samples exhibit a positive temperature coefficient of remanence α (=dM r /dT) from room temperature to about 600-700K, while positive temperature coefficient of coercivity β (=dH c /dT) is only observed in the alloys with low Cu content. It is found that the coercivity mechanism of the precipitation-hardened alloys varies with temperature and Cu content.