Abstract: As the richest source of astaxanthin, a natural antioxidant and coloring agent, the unicellular green alga, Haematococcus pluvialis, is being commercially exploited. A major constraint in the Haematococcus production system, however, is the thick, rigid cell walls associated with astaxanthin-rich cysts (or aplanospores). The thick walls prevent the extraction of cellular materials and consequently reduce the bioavailability of astaxanthin. Using a physical, chemical, or enzymatic method to disrupt the cell wall has proven to be very expensive and also introduce the risk of oxidation of astaxanthin by atmospheric oxygen The present invention provides a novel method for solving this problem by introducing two genetically modified Haematococcus pluvialis mutants. These two mutants, named as D 13-17 and N54-22, contain remarkably reduced amounts of cell wall materials, but retain the growth potential and ability to accumulate astaxanthin as high as the wild type strain.