PROBLEM TO BE SOLVED: To provide a method for simply and accurately estimating the nutritional state of a companion animal for each individual. SOLUTION: A step of collecting urine of an estimated companion animal, a step of quantitatively analyzing the creatinine concentration and the urea nitrogen concentration in the collected urine, and a step of measuring the creatinine concentration with respect to the urea nitrogen concentration in the analyzed urine A step of calculating a ratio (creatinine concentration/urea nitrogen concentration), and a step of estimating that the protein intake amount is insufficient when the ratio (creatinine concentration/urea nitrogen concentration) is larger than a preset predetermined value Have and. [Selection diagram] Figure 1【課題】伴侶動物の栄養状態を個体ごとに簡便且つ的確に推定する方法の提供。【解決手段】推定対象の伴侶動物の尿を採取する工程と、採取した尿中のクレアチニン濃度及び尿素窒素濃度を定量的に分析する工程と、分析された尿中の尿素窒素濃度に対するクレアチニン濃度の比率（クレアチニン濃度／尿素窒素濃度）を算出する工程と、前記比率（クレアチニン濃度／尿素窒素濃度）が予め設定された所定値より大きい場合には蛋白質の摂食量が不足していると推定する工程とを有する。【選択図】図１
