Present study involves investigation of Sulfamic acid as a catalyst for esterification of Phthalic anhydride with n- Butanol. Effect of different operating parameters such as molar ratio of reactants, catalyst quantity and operating temperature has been studied with an aim of optimization. The optimum parameters for this process have been found to be 1:.2 molar ratio of Phthalic anhydride to n-butanol, catalyst concentration of 6%(by weight) of reaction mixture and 130-180 degrees C reaction temperature. Maximum conversion levels of about 89% have been obtained in 1.5h of reaction time under these optimized conditions.