Results of anin situconduction ESR (CESR) study of HNO3molecule intercalation into highly oriented pyrolytic graphite (HOPG) plate with width being comparable with the graphite skin-depth governed by c-axis conductivity are presented. The stepwise changes of the intensity of CESR signal from intercalated parts of the HOPG plate is clearly detected during the intercalation. Using the chemical potential vs. intercalation time offered by the authors for the experimental conditions, this dependence was calculated theoretically.