The dependence of phase evolution on preparation conditions of precursor sols were investigated by DSC and XRD experiments during the sol-gel processing for Ba1-xSrxTiO3(BST) thin films. Two kinds of crystallization paths of perovskite BST were found during the annealing, which are closely dependent on chelating agent and solution aging. One path was the decomposition of all oxycarbonate intermediate, the other was the solid reaction between Ba/Sr carbonates and titanium oxides. For fresh sol, the addition of acetylacetone (HAcAc) as a chelating agent reduced the crystallization temperature by similar to 70 degreesC. Moreover, the back scattered scanning electron microscopy (BS-SEM) revealed that the HAcAc-derived films were homogeneous in composition in comparison with the heterogeneity of the films prepared with no chelating agent addition. The Variations mentioned above were considered originating from different molecule structures of the precursors.