Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy in combination with the sputter etching technique was applied to the determination of the depth distribution of a chemical additive within a pulp fiber. After etching successively, the surface additive content was determined by ATR-FTIR spectroscopy. Sputter etching until 5 min was homogeneous and proportional to obtain precise depth profile. From the relationship between etching time and the thickness of removed surface layer, it is possible to follow the partial concentration profiles of the additive as a function of distance from the original surface. The obtained profile is compared qualitatively with that of variable-angle ATR-FTIR depth profiling method. The profile shows that most of the additive is located at the fiber surface; however, some of it is broadly distributed toward the inside of the fiber. The present method can be used to clarify the distribution of other paper additives within a pulp fiber, and, moreover, it can be applied to depth profiling of a minor component within a solid material.