Intracellular digestion is a digestion which takes place within the cytoplasm of the organism.

Most organisms that use intracellular digestion belong to Kingdom Protista, such as amoeba and paramecium.

Lysosomes are organelles that contain hydrolytic enzymes that are used for intracellular digestion.

Intracellular digestion occurs in many unicellular protozoans, in Pycnogonida, in some molluscs, Cnidaria and Porifera.

Characteristics of intracellular digestion include an endosome fusing with a lysosome, releasing acid hydrolases which degrade DNA, RNA, proteins and carbohydrates.

Lysosomes carry out intracellular digestion, in a process called phagocytosis (from the Greek phagein, to eat and kytos, vessel, referring here to the cell), by fusing with a vacuole and releasing their enzymes into the vacuole.

In the late 1950s and early 1960s, de Duve and colleagues, using cell fractionation techniques, cytological studies and biochemical analyses, identified and characterized the lysosome as a cellular organelle responsible for intracellular digestion and recycling of macromolecules.