This study deals with supercritical CO2 extraction of astaxanthin from Haematococcus pluvialis with ethanol as an entrainer. The effects of pressure, temperature, CO2 flow rate, and the existence of the entrainer concentration on the amount of total extract, the amount of astaxanthin extracted, and the astaxanthin content in the extract were studied. Extractions were carried out at the pressures of 20-55 MPa, temperatures of 313-353 K, CO2 flow rates of 2-4 mL/min, and the ethanol entrainer concentrations of 1.67-7.5% (v/v). The amount of the total extract, astaxanthin extracted, and astaxanthin content in the extract increased with increasing temperature and pressure. With higher CO2 flow rate, the amount of the total extract could be increased while the amount of astaxanthin extracted and the astaxanthin content in the extract almost did not change. By using ethanol as an entrainer, a higher amount of astaxanthin extracted (80.6%) could be obtained at moderate pressure and temperature, and with the same conditions, the addition of the ethanol entrainer could more than twice enhance the amount of astaxanthin extracted. Without the ethanol entrainer, the highest astaxanthin extracted and astaxanthin content in the extract were 77.9 and 12.3%, respectively, and were obtained at high pressure and temperature.