Fucoxanthin, a major carotenoid of Cladosiphon okamuranus and other brown seaweed, exhibits anti-carcinogenic, anti-obesity, and anti-inflammatory activities. Despite these desirable activities, the utilization of fucoxanthin of a high purity in functional food preparations has been restricted because the instability of fucoxanthin makes its production difficult. In order to expand the industrial-scale use of C. okamuranus, the possibility of producing a fucoxanthin-rich product of a high purity was explored by using C. okamuranus as the source material. Several drying methods (hot-wind, vacuum, and freezing), drying temperatures (40-80ºC), and pulverization methods (particle size: 50, 200, and 1000 μm) were employed and the outcomes were compared; the conditions were optimized to minimize the decomposition of fucoxanthin. The 50 μm freeze-dried powder was found to be the best. In addition, the algal extract showed a strong DPPH radical scavenging activity.