Single event transient currents induced in 6H-SiC MOS capacitors are measured by using oxygen ions. Charges collected from the samples are calculated by the transient currents. Applying the drift-diffusion model to the charges, the diffusion length of electron is estimated. Transient currents induced in the gamma ray irradiated MOS capacitors are also investigated. No significant change in the transient currents is observed after gamma ray irradiation.