Mesoporous SrTiO3 was synthesized via the NaOH/KOH molten salt method. The detailed formation mechanism for the mesoporous SrTiO3 should be obtained to adjust the microstructure, which is an import factor affecting the photocatalytic activity. The detailed mechanism is explored by studying the intermediate phase. It is found that the NaOH/KOH molten salt method for mesoporous SrTiO3 synthesis, using four kinds of TiO2 with different morphologies as precursors, follows the precursor dissolution-precipitation growth mechanism. The mesoporous SrTiO3 structure originates from the reservation of space for NaOH/KOH. The crystallinity, number of pores, and size of particles are affected by the cleaning temperature, which can thus influence the photocatalytic activity.