This study was aimed at developing mass culture of Porphyridium creutum in a 5.0 L stirred photobioreactor. Effect of agitation and aeration rate on cell growth, extracellular polysaccharide product and cell ultrastructure were studied. Under the experimental photon flux density (1 000 μmol m -2 s -1) and temperature (25 ℃), the high growth and product of extracellular polysaccharide was observed at the agitation 200 r/min and aeration rate 0.71 vvm, and high aeration rate made biomass production and extracellular polysaccharide content increased. Comparing with the reciprocating shaker, the cells grown in the stirred photobioreactor contained greater number of starch grains, cytoplasmic vacuoles, chloroplast lamellae and thiner delatinous sheaths. The level of TC, TG and LDL-C in the rats fed with the diet containing P. cruentum biomass was significantly lower and the HDL-C level significantly higher than those in the high lipid control group. These results indicated that algae might be significant to control atherosclerosis and coronary heart disease. Fig 2, Tab 3, Ref 26