In this study, the preparation of titanium dioxide nanocrystals by sol-gel method has been considered. Then, the effect of modifier ligands such as acetylacetone (AcAc) and acetic acid (AcOH) on synthesis of TiO2 nanocrystalline powders has been investigated. The experimental results showed that the reaction of tetraisopropoxide titanium, Ti(OPri)(4), with acetylacetone and acetic acid leads to formation of complexes that can prevent the precipitation of undesired phases from highly reactive precursors. Whereas, the band of ligands to TiO2 nanocrystals is not broken easily at temperatures lower than about 400 degrees C. So these ligands may remain in the final TiO2 nanostructures and affect the morphology and structure of prepared materials. The studied samples were characterized using Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric and Differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM).