Antimony sulfoiodide (SbSI) is a highly efficient energy conversion piezoelectric material. We obtained SbSI doped with tin (II) ions according to the formula Sb_1-xSn_xSI_1-x (x=0.01–0.1). This heterovalent doping has been performed by the novel method of synthesis in an aqueous solution. The introduction of tin cations leads to a material Curie point increase of more than 10 K. The samples containing 5 mol.% of the dopant possess the best piezoelectric properties: piezomodule d₃₃～750 pC/N, dielectric constant at a frequency of 1 kHz — 1758, dielectric loss tangent — 0.054, and piezosensitivity — 50 mV × m/N. Thus, tin-doped SbSI is a promising material for highly efficient electromechanical transducers and sensors.