Abstract: The dielectric properties and phase transition of Sm3+-doped BaSn0.1Ti0.9O3 (BTS10) ceramics were investigated. The amount of Sm2O3 greatly affected the dielectric properties of BTS10. A dielectric constant of 5500 with 0.6mol% Sm2O3 and a dissipation factor of only 0.005 with 0.1mol% Sm2O3 were assessed. The variation in the dielectric constant indicated that Sm3+ ion is mainly substituted for the A-site ions when x≤0.6mol%, whereas it is mainly substituted for B-site ions when x exceeded 0.6mol%. Meanwhile, the variation in the dissipation factor showed that a very small amount of Sm3+ occupied the B site when x≤0.1mol%. The materials showed relaxor-like behaviour with a diffuse-type ferroelectric phase transition. The diffusivity increased when the amount of Sm2O3 is increased, which also implied that there should be a very small amount of Sm3+ occupying the B site when x≤0.1mol%. [Copyright &y& Elsevier]