A 66-year-old woman with SLE who recently started oral steroid was admitted to our hospital because of subacute numbness of the bilateral legs and gait disturbance, despite of the stable symptoms of SLE and its serology. Blood tests revealed hyperglycemia. Nerve conduction study showed decreased nerve conduction velocities consistent with demyelinative neuropathy. On initiation of insulin to control hyperglycemia, conduction velocities were rapidly increased in one week, suggesting hyperglycemic neuropathy. The rapid improvement of the conduction velocities was argued against mechanical "demyelination", rather suggesting axonal dysfunction, possibly associated with impaired function of Na(+)-K(+)-ATPase in hyperglycemic state.