In this study, astaxanthin from Haematococcus pluvialis has been extracted using supercritical CO2 and modified ethanol to obtain high concentrated of astaxanthin. The antioxidant activity of extract has also been tested by diphenyl pycril hydroxyl (DPPH) and measured by UV-Vis Spectrophotometer. The effect of prebure, temperature, CO2 flow rate and the existence of ethanol on total extraction yield, astaxanthin extracted and astaxanthin concentrated in the extract were studied. Extraction was carried out at 20-55 MPa of prebure, 313-353K of temperature, 2-4 ml/min of CO2 flow rate, 1.67-7.5 % volume of ethanol:CO2. The extract was analyzed by a Shimadzu Liquid Chromatograph LC-10AD, equipped with Diode Array Detector SPD-M10A and a 5C18-MS Waters of column. Maximum astaxanthin content in H. pluvialis sample was obtained by soxhlet extraction using dichloromethane as solvent. Maximum astaxanthin content was 3.43% weight. The amount of the total extract, astaxanthin extracted, and astaxanthin content in the extract increased with increasing temperature and prebure. Extraction yield increased with increasing CO2 flow rate, while the amount of astaxanthin extracted and the astaxanthin concentrated almost did not change with the increase in CO2 flow rate. The highest extraction yield, astaxanthin extracted and concentrated were obtained at high prebure and temperature. By using ethanol as an modifier, higher astaxanthin could be obtained at moderate prebure and high temperature. The addition of the modified ethanol could more than twice enhance the amount of astaxanthin extracted. The antioxidant activity of extract degraded with the existence of modified ethanol.