Tin (Sn)-doped beta phase gallium oxide (beta-Ga2O3) nanostructures at different Sn concentrations (0 to 7.3 at%) are synthesized using a facile hydrothermal method. The Sn-doped beta-Ga2O3 nanostructures are characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and absorbance spectroscopy. In addition, their photocatalytic activity is evaluated by observing methylene blue degradation under ultraviolet light (254 nm) irradiation. The photocatalytic activity of the Sn-doped (0.7 at%) beta-Ga2O3 nanostructures is significantly enhanced compared to that of intrinsic beta-Ga2O3 nanostructures due to the elevated charge separation. Excessive Sn concentrations (exceeding 2.2 at%) above the solid solubility limit of the Sn in beta-Ga2O3 nanostructures lead to SnO2 and SnO precipitation. The presence of SnO2 and SnO degrades the photocatalytic efficiency in the beta-Ga2O3 nanostructures. The results suggest new opportunities for the synthesis of highly effective beta-Ga2O3-based photocatalysts for applications in environmental remediation, disinfection, and selective organic transformations.