肌红蛋白（英语：Myoglobin）是由153个胺基酸环绕中央的血基质组成的单链蛋白质。分子量为16700道尔顿。其对氧气的亲合力大于血红蛋白，所以在肌肉组织中有保存氧气的功能。因为只需要一点氧分压便可以使其对氧气的结合力达到饱和，所以比血红蛋白更适合保存氧气。血基质对一氧化碳的亲和力比氧气大20000倍，但是因为肌红蛋白三级结构上His64（His E7）胺基酸不但与氧气可以产生氢键还可以使一氧化碳偏离原来的结合时的自然状态，在这一来一往的情形下，使得肌红蛋白对一氧化碳的亲和力只比氧气高出200倍。

Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. In humans, myoglobin is only found in the bloodstream after muscle injury. It is an abnormal finding, and can be diagnostically relevant when found in blood.