Abstract: Different month aged Japanese medakas (Oryzias latipes) were selected as  test species to compare acute toxicity effect made by Vanadium（Ⅴ）on adult fish and adolescent fish by using the semi-static bioassay method.The result showed that 72 h LC50 and 96 h LC₅₀ made by V（Ⅴ）on adult fish were 4.91 mg/L and 2.73 mg/L,and the safety concentration was 0.273 mg/L.72 h LC₅₀ and 96 h LC50 made by V（Ⅴ）on adolescent fish were 0.85 mg/L and 0.43 mg/L,and the safety concentration was 0.042 7 mg/L.Based on the criterion of toxicity made by toxic substances on fish,it is shown that V（Ⅴ）is moderate or highly toxic to Japanese medaka,and adolescent fish is more sensitive to its toxicity.

Key words: Vanadium (V), Janpanese medaka, acute toxicity, median lethal dose, afety concentationt