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The rheological properties and spectrum infrared of polysaccharides extracted from Cystoseira myriophylloides algae were investigated in the concentrations range from 3 to 9% (w/v) and at different temperatures. Results of rheological characteristics in a steady shear rate showed pseudoplastic properties and the dynamic rheological properties showed a fluid-like viscoelastic behavior. The flow and viscoelastic characteristics of polysaccharides were described using the power-law (the Ostwald model). The values of flow behavior index of the sample were close to unity (0.91) for 3% and it decreased up to 0.71 for 9% revealing the shear-thinning (pseudoplastic) nature of these polysaccharides. Moreover, the consistency coefficient increased non-linearly with concentration and it was described by a power law. The flow behavior as a function of temperature was satisfactorily described using the Arrhenius law and the activation energy values were extracted. It decreased from 15.68 and 17.21 kJ/mol when the concentration increased from 5 to 9% (w/v). Additionally, in dynamic rheological measurements, tan δ > 1 and G″ > G′ reveling a shear-thinning behavior. Finally, the analysis of the FTIR spectra of these polysaccharides showed the presence of uronic acid groups. This behavior would suggest that polysaccharides extracted from Cystoseira myriophylloides could be an interesting additive as thickeners. [ABSTRACT FROM AUTHOR]