多元不饱和脂肪是两类不饱和脂肪之一，分子中有多于一个双键，相比之下单元不饱和脂肪则只有一个双键，其余为单键。它必须从食物中摄取。常见的这类脂肪包括亚麻油酸及次亚麻油酸。红花籽油、粟米油、大豆油、葵花籽油及果仁均相对含有较多这类脂肪。这类脂肪在室温下呈液体状。

现代医学普遍认为，多元不饱和脂肪会同时降低低密度脂蛋白胆固醇（坏胆固醇，LDL）及高密度脂蛋白胆固醇（好胆固醇，HDL），相对比饱和脂肪健康，但容易令细胞老化。

Polyunsaturated fats are lipids in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds. Polyunsaturated fat can be found mostly in nuts, seeds, fish, algae, leafy greens, and krill. "Unsaturated" refers to the fact that the molecules contain less than the maximum amount of hydrogen. These materials exist as cis or trans isomers depending on the geometry of the double bond.