To provide a metal biocorrosion inhibitor that exhibits an effect at a low concentration and is excellent in biodegradability. A metal biocorrosion inhibitor comprising 3-methylglutaraldehyde as an active ingredient. [Selection figure] None【課題】低濃度で効果を発揮し、かつ生分解性にも優れる、金属の生物腐食抑制剤を提供すること。【解決手段】3-メチルグルタルアルデヒドを有効成分とする、金属の生物腐食抑制剤。【選択図】なし