Fission of 238U nuclei was performed by 45-69 MeV protons at the Cyclotron and Radioisotope Center of Tohoku University in Japan. The fission products originated in the reaction were identified by using gamma spectroscopy. The experimental data show that the charge distribution of isobar fission products follows a Gaussian distribution with a standard deviation independent of the selected mass number. The standard deviations were measured for the reaction 238U(p, f) with 45, 55, 65 and 69 MeV protons. For Ep < /sub> = 45 MeV, the standard deviation obtained from the experiment is in agreement with the existing data and satisfies the prediction of the Hauser-Feshbach statistical model. For other proton energies, measurement of this quantity has not been reported in the literature. The experimental results show that the value of standard deviation increases, when the excitation energy of the fissioning nucleus increases. Furthermore, the most probable charge was determined for the isobar fission products detected in the experiment. The results are consistent with the prediction of the minimum potential energy (MPE) model. Moreover, the experimental data show that nuclear charge polarization occurs in the fission process.