Alloy catalysts of Pt-Au/C with different Pt/Au ratios were prepared by the precipitation-deposition of metal chlorides and reduced by H(2) at 470 K. The surface composition of alloy crystallites deposited on the prepared catalysts was characterized by a technique of temperature-programmed reduction (TPR). In the characterization, O(2) was chemisorbed on the reduced catalysts and the chemisorbed O(2) was reduced by TPR. A low-temperature routine (LT) in the temperature range between 120 and 430 K was used for the TPR characterization. Monometallic catalysts of Au/C and Pt/C showed a reduction peak in the LT-TPR at reduction temperature (T(r))=145 and 240 K, respectively. T(r) from alloyed catalysts fell in the range and increased monotonously with their Pt/Au ratios. Interior Pt atoms in deposited alloy particles tended to segregate toward their surface during oxidation treatment at elevated temperatures.