Human, Trigeminal nerve, Motor root, Sensory root, Nerve fiber, Morphometry Summary: We evaluated the components of nerve fibers of the motor and sensory roots of the trigeminal nerve by morphometric analysis. Trigeminal nerves were obtained from 5 cadavers (males, aged 67-95) were stained by Masson-Goldner-Goto method and examined under the microscope using a morphometric image-analyzer. The area and perimeter of axons were larger in the motor root than in the sensory root. The size distribution of axons was wider in the motor root than in the sensory root and the distribution pattern was unimodal type. These findings suggested that nerve fibers of the human trigeminal nerve gave similar findings to those of other peripheral nerves, regarding axonal size distribution and relative size of motor and sensory nerve axons.