The middle colic vein lies in the abdomen alongside the middle colic artery. This vein drains blood from the transverse colon, which is the top portion of the large intestine.

The middle colic vein is a tributary of the superior mesenteric vein, which drains the small intestines. After accepting blood from its tributaries, the superior mesenteric vein joins with the splenic vein to form the hepatic portal vein. Because of this, the middle colic vein is considered to be part of the hepatic portal system.

Blood in the middle colic vein contains nutrients broken down by the large intestines. The oxygen content of blood in this vein is low because it has already passed through the large intestines. Blood from the middle colic vein travels along with blood from other branches of the hepatic portal system to the liver. The liver filters nutrients from this blood for processing.

Doctors sometimes use the middle colic vein as a point of catheter insertion for small children and infants undergoing liver cell transplants.