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Structure, exchange interaction, magnetic properties and magnetostriction of a series of cubic C15 MgCu2-type rare-earth transition-metal (R-T) compounds of Sm0.9Pr0.1 (Fe1-xAlx)(2) (0 less than or equal to x less than or equal to 0.2) have been studied by x-ray diffraction, A. C. initial susceptibility, vibrating samples magnetometer and standard strain technology. The substitution of Al for Fe leads to an expansion of the lattice parameter a by 5.1%. Curie temperature T-c is reduced continuously by replacing Fe with Al, which is ascribed to the decrease of the R-T coupling strength. The intersublattice coupling constant J(RT), molecular field coefficient n(RT), and exchange field B-ex, are evaluated by a molecular field model. The decrease of J(RT) with increasing Al content is related to the decrease of the number of (Sm, Pr)-Fe interacting pairs. Both the magnetostriction constant lambda (111) and the polycrystalline saturation magnetostriction lambda (s) at room temperature decrease with the Al addition, which can be ascribed to the decrease of the coupling strength.