上夸克（Up quark）是第一代夸克分类的一种。它拥有+(2/3)e的电荷，也是最轻的夸克，净质量介乎1.5到4 MeV之间。根据粒子物理学的标准模型理论，上下夸克是构成核子的基本元素，质子拥有两颗上夸克和一颗下夸克，而中子则有一颗上夸克和两颗下夸克。事实上，一颗核子的质量是以夸克间的胶子力主导，而非夸克本身的质量。

上夸克的存在最先于1964年提出，当时默里·盖尔曼 及乔治·茨威格制成了夸克模型。至1967年，透过SLAC直线加速器进行的深度非弹性散射实验，首度为这种夸克的存在提供了证据。

The up quark or u quark (symbol: u) is the lightest of all quarks, a type of elementary particle, and a major constituent of matter. It, along with the down quark, forms the neutrons (one up quark, two down quarks) and protons (two up quarks, one down quark) of atomic nuclei. It is part of the first generation of matter, has an electric charge of +⁄₃ e and a bare mass of 1.8–7000300000000000000♠3.0 MeV/c. Like all quarks, the up quark is an elementary fermion with spin-⁄₂, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle of the up quark is the up antiquark (sometimes called antiup quark or simply antiup), which differs from it only in that some of its properties have equal magnitude but opposite sign.