Time-resolved two-photon photoemission study has been performed on Si(111) surface at initial oxidation stage that is characterized by synchrotron-radiation photoemission spectroscopy. Transient 2PPE intensity from the conduction band minimum (CBM) shows a maximum at the delay time between 0.5 and 2ps depending on the oxygen dosage. The temporal profile of 2PPE intensity from surface state within the bulk band-gap shows a more rapid decrease than that on Si(001) surface, indicating that the metallic surface state on Si(111) surface causes the shorter lifetime of unoccupied surface state. The prolonged lifetime of 2PPE intensity from CBM after a large amount of O 2 exposure is caused by the disappearance of metallic surface state.