Resolution of racemic mandelic acid ((R,S)‐MA) and numerical determination of binary competitive isotherm of (R,S)‐MA on Chiralcel‐OD column have been investigated in this study. The effects of the alcohol modifier and acidic additive in the mobile phase on the retention and enantioseparation of (R,S)‐MA were studied at first. The inverse method was then used to determine the competitive isotherm parameters of (R,S)‐MA by minimizing the sum of square deviations of the model predictions from the measured elution profiles. The results indicate that the mobile phase with 85% hexane/15% isopropanol/0.3% trifluoroacetic acid mixture gives the best resolution of (R,S)‐MA and competitive‐modified Langmuir isotherm provides the more accurate sorption mechanism of (R,S)‐MA on the cellulose tris(3,5‐dimethylphenylcarbamate) chiral stationary phase.