Abstract: The nanocomposite permanent alloys which is composed of Pr₂(Fe,Co)₁₄B and α-(Fe,Co) and Pr₂(Fe,Co)₁₇ were made by single-roller rapid quenching. The X-ray diffraction method, room-temperature magnetic measurement and thermal magnetic analysis were used to analyze the microstructure and magnetic properties of Pr_7.5Dy₁Fe_86-xCo_xNb₁B_4.5(x=10,15) alloys. Magnetic properties of the ribbons annealing at different temperature and for various time were extensively studied. Permanent magnetic properties still keep a high level in the ribbons that were annealed at 700℃ for six hours. This result implies that thermal stability of the alloys may be enhanced by adding Co and Nb at the same time.