Amongst the diversity of pathways used by algae to reduce damage caused by ultraviolet (UV) radiation, the synthesis of UV-screening compounds is almost omnipresent. One class of sunscreen compounds that has been discussed in several reports is the production of mycosporine-like amino acids (MAAs). These compounds, which are present intracellularly in many marine and fresh-water organisms, are characterized by an aminocyclohexenone or aminocyclohexenimine ring with nitrogen or imino alcohol substituents.. Their strong UV absorption maximum between 310 and 360 nm and high molar extinction coefficients, sustain the hypothesis of a photoprotective role that has been demonstrated in a number of studies. To check the effects of UV-B radiation on the accumulation of MAAs, cultures of the red alga Gracilaria tenuistipitata were exposed for 72h to artificial UV-B radiation. Samples were collected each 6 hours and extract with MeOH 50%. The MAAs content and composition were investigated by high-performance liquid chromatography (HPLC) with the following conditions: l = 330 nm, flow = 1.0 mL.min^-1, C₁₈ column (5 mm, 250 x 4.6 mm, Phenomenex^®), mobile phase: binary gradient - MeOH and TFA 0.2%. The results showed an increase in the concentration of some MAAs in the cultures under UV-B radiation when compared with cultures under PAR. Our findings suggested that the macroalga G.tenuistipitata may protect itself from deleterious effects of UV-B radiation by their ability to synthesize photoprotective compounds.