The correlation between the PtPt interatomic distance of a Pt/C catalyst and the specific activity of the oxygen reduction reaction is discussed. Total X-ray scattering measurement coupled with pair distribution function (PDF) analysis was performed to obtain subsurface information of the Pt/C catalyst, which can obtain a much longer interatomic distance than X-ray absorption fine structure (XAFS) measurement. The subsurface structure of the catalyst was previously discussed on the basis of simulations with three-dimensional complex models. In this study, the subsurface structure of PtPt bonds in the catalyst could be easily obtained from experimental data by simple model fitting using the PDF. Results based on XAFS measurement showed no correlation with the specific activity. In contrast, the obtained PtPt interatomic distances in the subsurface using PDF showed a strong negative correlation with the specific activity as in a previous study.