The effects of oxygen annealing on the carbon content in MgO thin films were investigated, MgO thin films were deposited on Si(100) substrate at different temperatures of 400 to $700^{circ}C$ and different deposition rates of 3.4 to 11.6$AA$/min. Using rf magnetron sputtering method. Carbon content change on the surface of MgO thin films with the oxygen annealing at different temperatures was investigated using various method. The carbon content decreased as the annealing temperature increased. $Pb(Zr_{0.53}Ti_{0.47})O_3$(PZT) thin films were deposited on the MgO/Si(100) substrates. The effects of carbon content on the phase formation and the electrical properties of PZT thin films were also investigated.