Barite-celestite (BC) crystals were treated in highly concentrated alkaline hydrothermal fluid (5 M KOH) coexisting with a Ti(OH)(4)center dot 4.5H(2)O gel to produce SrTiO3 particles between 150 and 250 degrees C for several intervals between 6 h and 96 h. The BC transformation was initiated at a lower temperature (150 degrees C) and the total precursors consumption was completed at 250 degrees C for 96 h, resulting only in the crystallization of SrTiO3 particles. Different temperatures of reaction (<= 200 degrees C) lead to variations in morphology and particle size of the SrTiO3. The crystal growth of faceted cubic agglomerates was achieved at 250 degrees C, and it is provoked by the Oswald ripening mechanism. The release of barium to the hydrothermal fluid from the precursor occurred simultaneously with the transformation process. A low value of activation energy required for the single-step transformation of the BC plates into SrTiO3 particles was observed (26.33 kJ mol(-1)), under static hydrothermal conditions.