胞器（英语：organelle，或称胞器）是细胞的一部分， 是细胞中通过生物膜与细胞中其他部分分隔开来的、功能上独立的亚细胞结构，与细胞质基质和细胞骨架统称为“细胞质”。 细胞器可按各自拥有膜的层数大致分为三类(广义的细胞器还包括囊泡及核小体等)。

In cell biology, an organelle /ɔːrɡəˈnɛl/ is a specialized subunit within a cell that has a specific function. Individual organelles are usually separately enclosed within their own lipid bilayers.

The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells. While prokaryotes do not possess organelles per se, some do contain protein-based microcompartments, which are thought to act as primitive organelles.