Cellulose is the most abundant biopolymer and with different chemical modification products yields excellent properties like high viscosity, hydrophilicity, defoaming, chelating ability, etc. Carboxymethyl cellulose (CMC) is a product of carboxymethylation of cellulose being extensively used in food industry, agriculture, wastewater treatment, pharmacy and medicine. Despite, carboxymethylation lowers the thermal stability of the cellulose. This study focuses on investigating the thermal stability of CMC by crosslinking with polycarboxylic acids such as citric acid and fumaric acid. The crosslinking occurs between the hydroxyl groups of CMC and carboxylic groups of polycarboxylic acids via esterification, as confirmed by the presence of ester bands in FTIR spectra. The decarboxylation temperature of CMC is increased from 548 to 573 K in the crosslinked samples. The glass and crystalline phase transitions of CMC shifted to higher temperatures with the addition of crosslinkers. This suggests that the thermal stability of the CMC can be increased with crosslinking agents maintaining the properties of cellulose which would extend the application of CMC in various other fields. © 2019, Akadémiai Kiadó, Budapest, Hungary.