Objective　To provide micro-anatomical basis for recovering diaphragmatic function after cervical spinal injury by vagus nerve transposition to phrenic nerve.   Methods   10 healthy female SD rats were dissected to free the bilateral phrenic nerves, the vagus nerves and their branches under the surgical microscope. The distances between the vagus nerve and the phrenic nerve were measured by a sliding caliper(precision of 0.01mm) at "the phrenic nerve trunk originated level", "supraclavicula level" and "the level of diaphragma", and then the diameters of vagus nerves and phrenic nerves at the levels mentioned above were measured by microscope (precision of 0.0025mm) respectively.   Results    The diameter of vagus nerves was bigger than that of phrenic nerves by one third at the cervical part [the diameter of vagus nerve was （0.3284±0.0247）mm，phrenic nerve （0.2267±0.0164）mm], and the distance between them was no more than 2.5mm either at "the phrenic nerve trunk originated level" or at "supraclavicula level". At the "the level of diaphragma", the diameters of both nerves were roughly the same [vagus nerve was（0.2912±0.0326）mm，and phrenic nerve （0.2794±0.0282）mm], and at this level, the distance between them was (8.71±0.804) mm and (6.203±0.952) mm on the left and right sides respectively.   Conclusions    The diameters of vagus nerves and the phrenic nerves are not different so much in the cervical part. The two nerves get close to each other, therefore, it is possible to suture them directly without any tension, especially at "the level of diaphragma".