The novel flowerlike Bi7O9I3-MgAl2O4 nano-heterostructure photocatalysts with different mass percentages of Bi7O9I3 and MgAl2O4 were synthesized by the sono-solvothermal method. Synthesized samples were studied in the photocatalytic removal of MB under simulated solar light irradiation. Physical, chemical and optical properties of as-prepared photocatalysts were investigated utilizing characterization techniques such as XRD, FESEM, EDX, BET-BJH, FTIR, DRS and pHpze. Bi7O9I3(80)-MgAl2O4(20) nanophotocatalyst was identified as the optimum sample by removing 96.1% of methylene blue from water. The p-n heterostructure formation of Bi7O9I3-MgAl2O4 nanophotocatalyst led to increase the light absorption capability. Subsequently, it improved the separation of excited electron-hole pairs and reduced the recombination rate of them, which caused the higher photocatalytic activity of that sample than bare Bi7O9I3 and MgAl2O4. Moreover, the effects of initial solution pH, photocatalyst dosage, and initial dye concentration as efficient parameters on the photocatalytic performance were evaluated in this study. Finally, the reaction mechanism of methylene blue degradation from water was proposed.