苯丙氨酸（Phenylalanine，简称Phe或F），是二十种常见胺基酸的一种，化学式为：C₆H₅CH₂CH(NH₂)COOH，在室温下为粉末状固体。它是一种必需胺基酸，因为分子一端的苯环具有疏水性，所以苯丙胺酸被分类为非极性分子。L-苯丙胺酸(LPA)为一种电中性胺基酸，"UUU"和"UUC"是合成它的密码子。苯丙氨酸为酪氨酸，单胺类信号传导分子的多巴胺，去甲肾上腺素，和肾上腺素，以及皮肤色素的黑色素的前体。苯丙氨酸是在哺乳动物的乳汁中天然发现。它用于食品和饮料产品的制造，并作为以其著名的止痛和抗抑郁作用的营养补充剂出售。它是一种神经调节剂苯乙胺的直接前体，一种常用的膳食补充剂。 人体无法自行合成苯丙氨酸，必须从饮食中摄取，一般由植物生成苯丙胺酸，如下图：

Phenylalanine (US: /ˌfɛnəlˈæləniːn/, UK: /ˌfiːnaɪlˈæləniːn/; abbreviated as Phe or F) is an α-amino acid with the formula C₆H₅CH₂CH(NH₂)COOH. It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino acid is classified as neutral, and nonpolar because of the inert and hydrophobic nature of the benzyl side chain. The L-isomer is used to biochemically form proteins, coded for by DNA. The codons for L-phenylalanine are UUU and UUC. Phenylalanine is a precursor for tyrosine; the monoamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline); and the skin pigment melanin.