精氨酸（英语：Arginine）是一种α胺基酸，亦是20种普遍的自然胺基酸之一。在分子遗传学上，信使核糖核酸的结构，CGU，CGC，CGA，CGG，AGA和AGG。是在蛋白质合成时核苷酸碱基或遗传密码子代码为精氨酸的三元组。在哺乳动物生活中，精氨酸被分类为半必要或条件性必要的胺基酸(非必需胺基酸)，身体能自行产生，但在压力或疾病的时候，可能需要更多。也视乎生物的发育阶段及健康状况而定。早产儿体内不能合成精氨酸，使得补充他们营养中的精氨酸变得非常重要。于1886年精氨酸是首先由瑞士化学家恩斯特·舒尔茨从扁豆苗萃取物中分离出来。精液中80%由精氨酸构成，所以称之为精胺酸。

Arginine (abbreviated as Arg or R) encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH₃ form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO form under biological conditions), and a side chain of a 3-carbon aliphatic straight chain capped by a complex guanidinium, classifying it as a charged (at physiological pH), aliphatic amino acid. Arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual. Preterm infants are unable to synthesize or create arginine internally, making the amino acid nutritionally essential for them. Most healthy people do not need to supplement with arginine because their body produces sufficient amounts. Arginine was first isolated from a lupin seedling extract in 1886 by the German chemist Ernst Schultze.