We report the new evidence of the chemical modification of κ-carrageenan to its ester form using decanoyl chloride and pyridine, and by systematically varying the reaction temperature in the range from 60°C to 90°C. It was found that the percentage of yield of carrageenan esters is increased with the increase of synthesis temperature. Such results are also confirmed by both Fourier transform infrared (FTIR) and 1H NMR measurements. Thermogravimetric analysis (TGA) data showed that carrageenan esters are more thermally stable than κ-carrageenan. Carrageenan ester synthesised at 80°C is thermally more stable than all other carrageenan esters. Glass transition temperature (Tg) obtained by DSC analysis showed that the Tg values of carrageenan ester samples are lower than κ-carrageenan. The lowest Tg value, 83.15°C was obtained for the carrageenan ester sample synthesised at 90.0°C.