Novel and highly effective agents for suppressing fat accumulation and for suppressing body fat gain that contain astaxanthin and/or an ester thereof as an active component are provided. The agent for suppressing fat accumulation according to the present invention effectively suppresses accumulation of fat both in subcutaneous fat and in visceral fat. Even when high-fat diet intake is continued, body weight gain is suppressed by using the agent for suppressing body weight gain according to the present invention. Therefore, life-style related diseases, which are very likely to be caused by obesity, can be prevented, and the agents can be also used as an agent for preventing or alleviating a disease or a symptom having a relation to fat accumulation.