A material which has excellent ammonia metabolism improving effect and is effective for endurance enhancement, anti-fatigue or the like is provided. An ammonia metabolism promoting agent, comprising catechins and ornithine as active ingredients. An endurance enhancing agent, comprising catechins and ornithine as active ingredients. An anti-fatigue agent, comprising catechins and ornithine as active ingredients. An agent for suppressing a reduction in blood glucose level by exercise, comprising catechins and ornithine as active ingredients. An agent for promoting recovery from reduced blood glucose level by exercise, comprising catechins and ornithine as active ingredients. An agent for suppressing a reduction in muscle glycogen by exercise, comprising catechins and ornithine as active ingredients. A muscle endurance enhancing agent, comprising catechins and ornithine as active ingredients. An agent for preventing or ameliorating hyperammonemia, hepatic encephalopathy or chronic fatigue syndrome, comprising catechins and ornithine as active ingredients.