The chemical modification of native starch cause structural changes in the polymer molecule affecting their physic-chemical properties which make them suitable for various industrial uses. Tartaric acid is an organic dicarboxylic acid which can chemically modify the starch structure and its use is allowed in foods. Cassava starch was modified with tartaric acid and the effects of the concentration of the acid (4.5 – 8.0 g.100g-1) and pH of the reaction (5.0 – 8.0) on the starch were assessed by face-centered central composite design. The amylose and monoester tartrate content and swelling power and solubility were determined. The pasting properties and infrared spectra Fourier transform (FT-IR) was also evaluated. Increase in acid concentration and pH reduction decreased amylose concentration. There was a higher percentage of monoester tartrate of starch in the modification at pH 5.0. In pH 6.5 and 8.0, the modification improved pasting properties (greater thermal and mechanical resistance). FT-IR qualitatively confirmed the esterification of starch by bands associated with ester groups in assays with pH 5.0. Tartaric acid chemically modified the structure and properties of the cassava starch. Results showed that lower pH treatments enhanced starch esterification while higher pH promotes cross-linking.