The effects of annealing temperature and hydrolysis catalyst on the crystalline form and crystallite size of $TiO_2$ prepared by a sol-gel process were investigated. Three types of $TiO_2$ were synthesized by hydrolysis of titanium(IV)-iso-propoxide with water in n-propanol without catalyst (Type-A) and with HCl as catalyst, where the $H^+/Ti^{4+}$ mol ratio was 0.54 for Type-B and 0.2 for Type-C. Hydrolysis products were thermally treated at 100, 200, 300, 400 and 500 °C for 1 h after drying at room temperature. Characterization of the particles was carried out using XRD, BET, TG/DTA and SEM analysis. The pore size distributions were computed by the DFT plus method. The results showed that the acid catalyst and catalyst/alkoxide ratio have a large effect on the formation of anatase $TiO_2$. In particular, it was found that anatase phase $TiO_2$ particles occur at 400 and 500 °C for Type-A $TiO_2$, while they do so at nearly 200 °C for Type-B and Type-C $TiO_2$. The crystallite size of Type-A, Type-B and Type-C increased from 17.96 to 19.24 nm, from 12.38 to 15.12 nm and from 10.60 to 12.20 nm, respectively, when the thermal treatment temperature was raised from 400 to 500 °C.