Haematococcus pluvialis, the best natural source for astaxanthin, was cultivated with an immobilized biofilm method, viz. "attached cultivation", which was high in photosynthetic efficiency. A practical operational protocol for this "attached cultivation" method was investigated by studying the effects of inoculum density, light intensity, nitrogen quantity as well as medium volume on growth and astaxanthin accumulation. Results indicated the optimized inoculum density and light intensity were 10 g m(-2) and 100 mu mol m(-2) s(-1), respectively. The optimized nitrogen supply strategy was circulating ca. 30 L of BG-11 medium with initial sodium nitrate concentration of ca. 1.8 mM for 1 m(2) of cultivation surface. With this strategy, the maximum astaxanthin productivity reached ca. 160 mg m(-2) d(-1) which is much higher than many other indoor researches. Both of the red and green cells were found in the biofilm with red cells on the top. (C) 2014 Elsevier Ltd. All rights reserved.