Phase transition, dielectric properties, and leakage current characteristics of Ta2O5 thin film fabricated by sol-gel process with tantalum penta-n-butoxide were studied as a function of annealing temperature in O2 atmoshpere. Although Ta2O5 thin film annealed at temperatures below 700$^{circ}C$ for 1 hr was amorphous, it was crystallized to ${eta}$-Ta2O5 of orthorhombic phase by annealing at temperatures higher than 750$^{circ}C$. With increasing annealing temperature from 500$^{circ}C$ to 900$^{circ}C$, dielectric constant of sol-gel processed Ta2O5 thin film was changed from 17.6 to 15.3 due to the increase of SiO2 thickness at Ta2O5/Si interface. For Ta2O5 thin film annealed at 500$^{circ}C$ to 800$^{circ}C$ for 1 hr in O2 atmosphere, leakage current was remarkably reduced and breakdown strength was increased with higher annealing temperature. For Ta2O5 film annealed at 800$^{circ}C$, breakdown did not occur even at electric field strength of 30${ imes}$105V/cm and leakage current was maintained lower than 10-8A/$ extrm{cm}^2$.