Acetylacetone is used as a chelating agent for titanium(IV) isopropoxide to inhibit hydrolysis and stabilize the precursor solution. The effect of the molar ratio between titanium(IV) isopropoxide and acetylacetone of 1:1, 1:2, 1:3 and 1:4 in the precursor solution on the morphological, structural and optical properties of TiO2 thin film was investigated. These properties were studied using Fourier transformed infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and UV–vis spectroscopy as a function of the molar ratios for the as-deposited thin films and films annealed at temperatures of 700, 800 and 950°C. Mixed anatase and rutile phases were detected after annealing at 800°C for 1:1 and 1:2 molar ratios and at 700°C for 1:3 and 1:4 molar ratios. The optical band gap decreased from 3.45 to 3.02eV with an increase in the annealing temperature in agreement with corresponding structural changes. •The grain sizes of TiO2 thin films could be varied over the range of 20 to 210nm.•TTIP and AcacH ratio affects the transformation process from anatase to rutile.•TiO2 bandgap decreased from 3.45 to 3.02eV with an increase in annealing temperature.