The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge experiment under conditions that a gravitational field of 0.81 × 10⁶G for 100 hours at 150°C (solid state) in our previous study. The isotope fluctuation on this sample was measured using secondary ion mass spectrometer (SIMS). The ¹¹⁵In/¹¹³In isotope ratio changed with positive gradient in the direction of centrifugal force approximately 1.2%. The isotope ratio fluctuation of centrifuged sample was 4 times larger than that of starting sample (<0.3%). This showed that the isotope fractionation effect was induced by solid centrifugation in this alloy, although achieved concentration gradients were small.