Titanium (Ti) atom densities on the radial and axial directions in Ar-O-2 reactive rf (13.56 MHz) magnetron sputtering were investigated by an atomic absorption method for the conditions where crystalline TiO2 films grow. Ti atom densities in pure Ar discharge were also measured for comparison with those in the Ar-O-2 mixture discharge. At a total pressure of 3.5 Pa and rf power of 200 W, the Ti atom densities in the Ar-O-2 discharge were (0.2-3.1) X 10(9) cm(-3), two orders smaller than those [(0.2-2.2)X 10(11) cm(-3)] in pure Ar discharge in the measured region. On the other hand, the Ti atom densities in the Ar-O-2 discharge at a total pressure of 0.35 Pa were (0.2-2.9) X 10(9) cm(-3), while those were (0. 1-1.0) X 10(10) cm(-3) in the pure Ar discharge at 0.35 Pa. Radial profiles of the Ti atom density with a peak structure in Ar-O-2 and pure Ar were interpreted based on the plasma parameters and self-bias voltage.