An analytical method for a rapid reverse-phase liquid chromatography of amino acids is presented. The total analysis time was 19 min. The average relative deviation over the measured peak area was lower than 10% and the fluorescent response was linear with concentration for OPA derivatives (r > 0.99) in the range 100-1000 nM. The proposed method was applied to the determination of free amino acids in two microalgae species (Chlorella pyrenoidosa and Chlamydomonas rinhardtii). The principal aminoacids found were alanine, arginine leucine, serine and glutamic acid.