Nutritional composition is analysed for the red microalga Porphyridium cruentum cultured under various conditions in an external tubular photobioreactor. The data include the proximate composition (moisture, ash, crude protein, available carbohydrates, fiber, lipids and energy), nitrate, RNA, mineral elements (Na, K, Ca, Mg, Fe, Cu, Zn, Mn, Cr, Mn, Co, S, As, Pb, Cd), C/N ratio, fatty acids and pigments (carotenoids, phycobiliproteins, chlorophylls and degradation products). On average, the biomass contains 32.1% (w/w) available carbohydrates and 34.1% crude protein. The mineral contents in 100 g dry biomass were: Ca (4960 mg), K (1190 mg), Na (1130 mg), Mg (629 mg) and Zn (373 mg). Toxic heavy metal contents were negligible. The fatty acid contents were (in percent dry wt): 1.6% of 16:0; 0.4% of 18:2ω6; 1.3% of 20:4ω6 and 1.3% of 20:5ω3. Nutrient composition of biomass was highly influenced by residence time in the bioreactor and the external irradiance. The biomass collected for short residence times was richer in protein and eicosapentaenoic acid.