What's the Smallest Organ in the Human Body?

The smallest organ in the human body is the pineal gland. Located deep within the brain, between the two hemispheres, this tiny, pea-shaped organ is about the size of a grain of rice, typically measuring between 5 and 8 millimeters in length. Despite its small size, the pineal gland plays a critical role in regulating sleep-wake cycles by producing melatonin, a hormone that helps control circadian rhythms.

While other structures in the body, such as the stapes bone (the smallest bone) or the stapedius muscle (the smallest muscle), are even smaller, the pineal gland is recognized as the smallest organ—a distinct structure with a specific function made up of multiple tissue types.