The test particle method proposed by Widom was applied to calculate the solubilities of naphthalene in supercritical carbon dioxide at 308.15 and 328.15 K. The Lennard-Jones (12-6) potential was used as the intermolecular potential. The solubilities of naphthalene in supercritical carbon dioxide have been calculated quantitatively by introducing two binary interaction parameters k(12) and l(12) between unlike molecules. The binary interaction parameter k(12) is used to calculate the energy parameter epsilon(12), while l(12) is used to calculate the size parameter sigma(12). The calculated results by the Monte Carlo simulation show in good agreement with the experimental data.