We investigated magnetic field-induced strain (MFIS) due to conversion of martensite variants of a disordered Fe-31.2Pd(at.%) single crystal and an ordered Fe3Pt single crystal exhibiting martensitic transformations from cubic phases to tetragonal phases at 230 K and 85 K, respectively. The tetragonality c/a of Fe-31.2Pd is 0.940 at 77 K and that of Fe3Pt is 0.945 at 14 K. MFIS was measured by applying magnetic field along the [001](p) (the symbol "P" stands for the parent phase) direction. When magnetic field is applied, the specimen expands along the field direction for Fe-31.2Pd and contracts for Fe3Pt, suggesting that the c axis is the hard axis of magnetizaion for Fe-31.2Pd and is the easy axis for Fe3Pt. Conversion of variants by magnetic field is almost perfect for Fe-31.2Pd but is not perfect for Fe3Pt. In addition, a large recoverable MFIS appears in Fe3Pt, which depends on temperature and shows a maximum value of nearly 1% at 40 K.