Phycobiliproteins are light harvesting pigment proteins involved in light absorption during photosynthesis in microalgae Arthrospira platensis. According to their absorbance spectrum we distinguish between three representatives: phycoerythrin, phycocyanin and allophycocyanin. Since the lactic fermentation of a substrate can affect the profile and activity of its bioactive components, we investigated the effect of lactic fermentation on purity ratio and antioxidant activity of phycobiliproteins in vitro and in vivo. Lactobacillus plantarum was used for fermentation of microalgal biomass. The extracts of fermented and nonfermented biomass were prepared by two different extraction methods; mechanic and nonmechanic. Phycobiliproteins in extracts were further purified by two-phased ammonium sulphate precipitation. Analysis were performed both on extracts and precipitated phycobiliproteins. Results of nonmechanic extraction method did not show differences in purity ratio of phycobiliproteins between the extracts of fermented and nonfermented microalgae, whereas in precipitated phycobiliproteins purity ratio of all representatives obtained from fermented microalgae were higher compared to the nonfermented microalgae. After fermentation the in vitro antioxidant activity of precipitated phycobiliproteins was higher compared to precipitated phycobiliproteins before fermentation. The antioxidant activity in vitro of extracts did not differ between fermented and nonfermented microalgae. The in vivo antioxidant activity at given concentration did not differ between precipitated phycobiliproteins from fermented and nonfermented microalgae compared to controls. With mechanic extraction method neither extracts nor precipitated phycobiliproteins differed in purity ratio of fermented and nonfermented microalgae. Moreover, the in vitro antioxidant activity of microalgae extracts and precipitated phycobiliproteins did not differ between fermented and nonfermented microalgae, as well as the in vivo antioxidant activity at a given concentration did not differ between precipitated phycobiliproteins from fermented and nonfermented microalgae compared to controls.