吞噬细胞（俄语：Фагоцит，英语：phagocyte）是透过吞噬有害的外来微粒、细菌及坏死或凋亡细胞（即噬菌作用）以保卫人体的白血球。它的命名源自希腊文「phagein」（吃或吞食）及「-cyte」（生物学中代表细胞的后缀），是对抗传染病不可或缺的细胞，也是后天免疫力的组成之一。吞噬细胞在整个动物界中作用重大，并在脊椎动物中高度发展。一公升的人血内含有约六百万个吞噬细胞。1882年，埃黎耶·埃黎赫·梅契尼可夫在研究海星幼虫时首度发现了吞噬细胞，梅契尼可夫并因此获得1908年诺贝尔生理学或医学奖。吞噬细胞存在于许多物种中；有些阿米巴原虫功能表现类似于巨噬细胞，可推测吞噬细胞可能在生命演化初期便已存在。

Phagocytes are cells that protect the body by ingesting (phagocytosing) harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek kutos, "hollow vessel". They are essential for fighting infections and for subsequent immunity. Phagocytes are important throughout the animal kingdom and are highly developed within vertebrates. One litre of human blood contains about six billion phagocytes. They were first discovered in 1882 by Ilya Ilyich Mechnikov while he was studying starfish larvae. Mechnikov was awarded the 1908 Nobel Prize in Physiology or Medicine for his discovery. Phagocytes occur in many species; some amoebae behave like macrophage phagocytes, which suggests that phagocytes appeared early in the evolution of life.