单元不饱和脂肪（英语：monounsaturated fat）是两类不饱和脂肪酸之一，分子中只有一个双键，其余皆为单键；相比之下，多元不饱和脂肪酸则有多于一个以上的双键存在例如二十花生四烯酸。单元不饱和脂肪酸是属于非必需脂肪酸（non-essential fatty acids），可以在体内合成，例如ω-9（Omega-9）系列脂肪酸。常见的此类脂肪酸包括棕榈油酸或油酸，油酸是橄榄油与棕榈油的主要成份之一，而芥花籽油、花生油、菜籽油、果仁及牛油果等植物油均相对含有较多这类脂肪酸。

In biochemistry and nutrition, monounsaturated fatty acids (abbreviated MUFAs, or more plainly monounsaturated fats) are fatty acids that have one double bond in the fatty acid chain with all of the remainder carbon atoms being single-bonded. By contrast, polyunsaturated fatty acids (PUFAs) have more than one double bond.