灰鯖鮫（Isurus oxyrinchus）為一種於全球溫帶與熱帶海域棲息之魚種，本研究使用南大西洋海域（0°22´ N - 38°53´ S，49°06´ W - 12°47´ E）2011年5月到2014年8間月臺灣鮪延繩釣遠洋觀察員所採集之灰鯖鮫脊椎骨進行年齡與成長參數推估。脊椎骨矢狀切片採用X-ray照射並計算明暗帶輪紋數。所使用樣本雌魚140尾、雄魚128尾。本種之成長經最大概似法檢定雌雄間存在顯著差異（P<0.05）。從邊緣成長率變化推測本魚種之成長週期為一年，不透明帶在10月形成。以非線性迴歸評估von Bertalanffy with size at birth成長參數為雌魚極限體長L∞ = 392.7 cm FL、成長係數k = 0.0367/yr；雄魚為極限體長L∞ = 327.9 cm FL、成長係數k = 0.0484 /yr。灰鯖鮫雄魚在0-4歲間之成長速率高魚雌魚，之後則顯是雌魚高於雄魚。雌魚之最大觀測體長（tmax）為313公分，雄魚則為250公分，最大觀測年齡雌、雄分別為35歲與21歲。 The shortfin mako（Isurus oxyrinchus）is an epipelagic species distributed in temperate and tropical seas. Growth band pairs were counted on sagittal slice vertebral centra by using a X-ray method.The specimen collected by observers in Taiwanese longline fisheries is used for age and growth analysis. Between May 2011 to Aug. 2014, 140 female and128 male were captured in south Atlantic（0°22´ N - 38°53´ S, 49°06´ W - 12°47´ E）. Marginal increment analysis indicated that annual opaque band formed during October. Applied the Likelihood ratio test, the von Bertalanffy growth function between female and male revealed which in south Atlantic was significant different（P<0.05）. von Bertalanffy with size at birth parameters estimated as following estimates: L∞ = 392.7 cm FL、k = 0.0367/yr for female; L∞ = 327.9 cm FL、k = 0.0484 /yr for male. From age 1 to 4, the growth rate of males is larger than that of females, thereafter, females showed a significantly larqer growth rate compared to females. Maximum length observed was reached at age 35 and 313 cm FL for female, and age 21 and 250 cm FL for male.