Astaxanthin, a valuable antioxidant in nutraceuticals and cosmetics, can be produced in significant quantities from the well-known source Haematococcus pluvialis. However, high-quality antioxidant extracts from microalgae cannot be obtained through traditional solvent extraction techniques, which also require solvent recovery and significant purity. Therefore, supercritical CO2 extraction (SC-CO2) can serve as an effective alternative for selectively isolating valuable constituents from a preliminary pigment extract mixture. Supercritical CO₂, when combined with polar solvents, can enhance polarity for higher purity and selective extraction. It is particularly suited for biological extraction due to its low critical temperature (31 °C), moderate pressure requirement (73.8 bar), and numerous advantages, including its nontoxic, bacteriostatic, eco-friendly, and nonflammable properties, as well as its affordability and widespread availability in pure form. To date, supercritical CO2 extraction has significantly impacted industries such as food, cosmetics, and pharmaceuticals thanks to its high speed (10–60 min), minimal solvent residue, and uncomplicated process. This chapter discusses the up-to-date, step-wise procedure for the extraction of astaxanthin by supercritical CO2 extraction from the biomass of H. pluvialis, with its key considerations and critical information.