Abstract The biological assimilation of the sugars present in lignocellulosic residues has gained prominence since these residues are the most abundant and economic residues in nature. Thus, the objective of this work was to determine whether the use of D-xylose and L-arabinose as sources of carbon in Synechococcus nidulans and Spirulina paracas cultures affects the growth and production of proteins and carbohydrates. Kinetic growth parameters, pentose consumption, protein content and carbohydrates were evaluated. Synechococcus nidulans and Spirulina paracas consumed all concentrations of pentose used. The highest cellular concentration (1.37 g.L-1) and the highest protein productivity (54 mg.L-1.d-1) were obtained for Spirulina paracas, which was submitted to the addition of 38.33 mg.L-1 D-xylose and 1.79 mg.L-1 L-arabinose. The use of pentose promoted the accumulation of proteins for the studied microalgae. This is one of the first works to report protein bioaccumulation as a result of pentose addition.