Water sorption isotherms are important tool for designing the technological processes and predicting stability and shelf life of food. The aim of the work was to determine the water sorption isotherms of commercial furcellaran at different temperatures (20, 35 and 50 °C) using a gravimetric method under different levels of relative humidity (19-95%). The experimental data obtained have been interpreted in the terms of various isotherm models and it was found that the best results were obtained with the Peleg model (P < 2.1%; RSME <0.01; R2 = 1.00). The obtained isotherms followed the type II pattern and, in all cases, the sorption capacity increased with increasing water activity and decreased with increasing temperature. The maximum net isosteric heat for adsorption and desorption was 938.9 and 988.6 J g -1, respectively, at an equilibrium moisture content of 0.05 gw gdb -1. The net isosteric heat of sorption decreased exponentially with increasing moisture content and approached zero at 0.26 gw gdb -1 for adsorption and 0.32 gw gdb -1 for desorption. The developed mathematical relationships can be used to optimize the drying processes and storage conditions of furcellaran.