单核吞噬细胞系统（英语：Mononuclear phagocyte system、MPS）是高等动物免疫系统的一部份，由可以进行吞噬作用的细胞组成 。通常存在于网状结缔组织（reticular connective tissue）。这些吞噬细胞都来自骨髓的干细胞，先发育成单核球与巨噬细胞，累积于淋巴结与脾脏中，吞噬细胞可受趋化因子吸引，以变形虫运动穿透微血管，移至其他组织并发育成特化的巨噬细胞，如肝脏的库佛氏细胞、组织中的组织细胞（Histiocyte）、神经系统中的微胶细胞、骨骼的蚀骨细胞、胸膜与腹膜的巨噬细胞与肺的尘细胞等都是单核吞噬细胞系统的一部份，并依不同组织而有不同功能。

In immunology, the mononuclear phagocyte system (MPS) (also known as the reticuloendothelial system or macrophage system) is a part of the immune system that consists of the phagocytic cells located in reticular connective tissue. The cells are primarily monocytes and macrophages, and they accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the MPS. The mononuclear phagocyte system and the monocyte macrophage system refer to two different entities, often mistakenly understood as one.