Abstract In this paper, the structure and magnetostriction of melt-spun Pr 0.3Tb 0.7Fe 2B x ( x = 0–0.3) alloys are investigated. The result of X-ray diffraction shows that there are amorphous phase in all melt-spun samples before annealing, while all samples except B-free alloy crystallize into the REFe 2 crystal structure with no evidence of any secondary phase after being annealed at 773 K for 30 min. It is found that the crystalline structure changes greatly though the melt-spun ribbons are annealed for only a few minutes. The saturation magnetization changes modestly with B concentration changing. The magnetostriction of bonded Pr 0.3Tb 0.7Fe 2B x composites at 11 kOe increases with B concentration increasing.