The carbon and oxygen on the Mo (110) surface has been investigated by means of LEED and AES. We found that, after argonion bombardment of Mo (110) surface containing carbon and oxygen with the beam energy 1 keV and beam current 6μA, the Auger, peak shapes and carbon intensities changed. Depth-profile technique showed that carbon was diffused from the bulk. Heating sample to temperature above 700 ℃ or 750℃, two types of LEED patterns of Mo(110) c(4×4)-C, (-4 2 2 2) -C were observed respectively.