We have succeeded in growing epitaxial CrO 2 (110) thin films on MgO(001) substrates with TiO 2 (110) buffer layers oxidizing from TiN(001) thin films. Thin TiN(001) epitaxial films grown by reactive dc-magnetron sputtering were transformed into TiO 2 (110) with an annealing process in low-pressure oxygen, followed by selective CrO 2 (110) growth on TiO 2 buffer layers by chemical vapor deposition. X-ray diffraction experiments and scanning electron microscopic observation revealed that the epitaxial relationship of the sample is MgO (001)[110] k TiO 2 (110)[001] k CrO 2 (110) [001]. Both the CrO 2 (110) films and TiO 2 (110) buffer layers are orthogonally twinned and formed with small grains of CrO 2 of 3 -5 mm size and of TiO 2 of sub-mm size.