A simple, developed, fast, and accurate spectrophotometric method was examined to determine Mesalazine (MES) in its pure form and pharmaceutical preparation (Pentasa). It was based on the formation of an ion pair complex between MES and the Amaranth (AMA) reagent to give a purple color product which gives its highest absorption at the wavelength of 556 nm. The best conditions for complex formation were found (time, temperature, optimal reagent concentration, and pH). The linearity of the method for the complex consisting ranged from 5-45 µg/mL, the Sandell's index was 0.01934 µg/cm2, the molar absorption coefficient was 7917.338 L/mol.cm and the detection limit was 0.03772 µg/mL, the quantitative limit was 0.11432 µg/mL, the percent recovery range was Rec% between (100.9671-95.5512) %, and the relative standard deviation rate RSD% between (0.3752-0.2926)%. It was found that the method is accurate and precision and has been successfully applied to estimate the MES in its pharmaceutical preparation, in direct methods, and in multi standard additions.