Culex pipiens (Cx. pipiens) or common house mosquito is the most widely distributed species worldwide, including Saudi Arabia. The current study examined morphological, histological, and ultrastructural features of midgut epithelium of fourth instar larvae of Cx. pipiens. Findings provide a basis for research on insecticide resistance and mosquito control. The morphological, histological and ultrastructural studies used both light and transmission electron microscopy. Morphologically, the external features of the body of the larva show three main regions, head, thorax and abdomen, with 10 externally visible segments. The digestive tract includes foregut, midgut and hindgut. Histologically, the midgut is lined by a single layer of cuboidal or low columnar epithelial cells associated with intercalated regenerative cells scattered. All cells rest on a thick basement membrane. Ultrastructurally, cuboidal to low columnar cells of the midgut of fourth larval instar shows absorptive cells with apically well-developed striated borders of microvilli and large rounded central nuclei, resting on a thick basement membrane. Thin intercalated regenerative cells are scattered among epithelial cells. The apical cytoplasm epithelial cells display numerous mitochondria, rough endoplasmic reticulum, vacuoles and secretory vesicles. A distinct peritrophic membrane is seen that acts as a protective barrier between haemolymph, midgut cells and food contents. The current study concludes that Cx. pipiens fourth instar larva midgut lined by a single layer of broad cuboidal to low columnar epithelial cells with large spherical nuclei, numerous mitochondria, lysosomes and secretory vesicles, and apical regions with well-developed brush borders of microvilli. They rest on a thick basement membrane and associated with isolated regenerative intercalated cells.