The research presents esterification of octanoic acid and trimethylolpropane (TMP) by using H₃PW₁₂O₄₀ supported on montmorillonite in supercritical carbondioxide (SCCO₂). This research investigated the effects of temperature, TMP to octanoic acid molar ratio, amount of catalyst and chain length of fatty acids on TMP conversion and selectivity of mono-, di-, triester. It was found that decreasing of TMP/fatty acid molar ratio promoted TMP convertion and selectivity of triester due to the TMP absortion on catalyst surface was reduced. The increasing amount of catalyst also enhanced TMP conversion and selectivity of triester because the increasing of surface area and active site. The TMP conversion and selectivity of trimester was risen with increasing temperature and reaction time. The shot chain fatty acid promoted TMP convertion and selectivity of triester due to it can be easily diffused into catalyst pore. However, selectivity of triester in atmospheric pressure with varying nitrogen of 50 ml/min was more than that produced in SCCO₂ because nitrogen carried water away from the reaction. On the other hand, amount of adsorbed organic on catalyst in SCCO₂ was less than in nitrogen atmospheric due to SCCO₂ the heat and mass transfer properties is SCCO₂ was better than nitrogen atmospheric. The optimal reaction conditions were trimethylolpropane/octanoic acid molar ratio of 1:4 reaction temperature of 150 °C, catalyst amount of 8 wt% of trimethylolpropane and reaction time of 8 h. in atmosphere addition with nitrogen flow.