The surfaces of TiC(111) and TiC(111)-( 3 × 3 )R30-O were investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and DV-Xα calculation. Atomically resolved STM images of an oxygen-adsorbed surface were observed to have bright spots with a ( 3 × 3 )R30 periodicity. The STM image contrast was invariant with respect to the polarity of the sample bias voltage. The STM images and the calculation results are discussed in terms of surface geometry and local electronic state.