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Structure and magnetostriction of Dy1-xPrxFe2 (0 ≤x≤0.5), Dy0.6Pr0.4(Fe1-yTy)2 (0＜y＜0.6), and Tb1-zPrz(Fe0.4Co0.6)2 (0≤z≤1.0) alloys (T＝Co, Ni) have been investigated. It is found that the matrix of the alloys Dy1-xPrxFe2 is a single phase (Dy, Pr)Fe2 with MgCu2-type structure and the second phase is (Dy, Pr)Fe3 when x≤0.2. The amount of (Dy, Pr)Fe3 phase increases with increasing Pr content and becomes the main phase when x＝0.4. The matrix of Dy1-xPrxFe2 is found to be the (Dy, Pr)2Fe17 phase with Th2Zn17-type structure when x＝0.5. It is found that the amount of the cubic Laves phase (Dy, Pr)(Fe, Co)2 in the Dy0.6Pr0.4(Fe1-yCoy)2 increases with increasing Co concentration when 0≤y≤0.6. The substi tution of Ni for Fe is nearly not favorable for the formation of the cubic Laves phase (Dy, Pr)(Fe, Ni)2 in (Dy1-xPrx)Fe2. The matrix of (Tbl-zPrz)(Fe0.4Co0.6)2 is a (Tb, Pr)(Fe, Co)2 phase with the MgCu2-type cubic Laves structure and a second phase of small amount is (Tb, Pr)(Fe, Co)3 phase when z≤0.2, z＝0.5 and 1.0. When 0.2＜z≤0.4, the amount of the (Tb, Pr)(Fe, Co)3 phase with PuNi3-type structure increases with increasing z and becomes the main phase when z＝0.4. When 0.5＜z≤0.6 the amount of the (Tb, Pr)(Fe, Co)3 phase increases sharply, whereas for 0.6＜z≤0.8 it decreases with increasing z. The polycrystalline magnetostriction, λ‖ － λ┴, at room temperature of Dy1-xPrxFe2 exhibits a peak when x＝0.3. The λ‖ - λ for Dy0.6Pr0.4(Fel-yMy)2 (M＝Co, Ni) and Tb1-zPrz(Fe0.4Co0.6)2 is also examined.