AbstractWheat bran is modified thermochemically through reaction with citric acid, as carboxyl groups bearing agent, according to a dry condition method at the elevated temperature. In this study, the main objectives are optimization the factors affecting on the pendant carboxylic acid groups of wheat bran–citrate, including concentration of citric acid solution (0–1.8 M), volume of citric acid solution (5.4–16.2 g), curing temperature (0–170 °C), curing time (0–90 min.), mixing method (solution mixing vs kneading) of reactants, and the catalyst effect (0–5, sodium phosphate dibasic dodecahydrate/citric acid molar ratio). The amount of pendant carboxylic acid groups is determined by simple acid-base titration. The obtained methylene blue adsorption data is well matched with the amount of pendant carboxylic acid groups in wheat bran–citrate and this amount increase with an increase in pendant carboxylic acid groups.