Age-associated changes in neuromuscular function may be due to a loss of motor neurons as well as changes in their biophysical properties. Neuronal damage imposed by reactive oxygen species may contribute to age-related deficits in CNS function. Thus, we hypothesized that aging would alter the functional properties of motoneurons and that caloric restriction would offset these changes. Intracellular recordings were made from lumbar motoneurons of old Fisher Brown Norway (FBN) fed ad libitum (oldAL, 30.8±1.3mo) or on a fortified calorie-restricted diet from 14-weeks of age (oldCR, 31.0±1.8mo). Basic and rhythmic firing properties recorded from these aged motoneurons were compared to properties recorded from young FBN controls (young, 8.4±4.6mo). Compared to young MNs, old MNs had a 104% greater (p<0.001) afterhyperpolarization potential (AHP), a 21.1% longer AHP half-decay time (p<0.05), 28.7% lower rheobase (p<0.001), 49.7% greater (p<0.001) input resistance, 21.1% (p<0.0001) less spike frequency adaptation, lower minimal (30.2%, p<0.0001) and maximal (16.7%, p<0.0001) steady-state firing frequencies, a lower (35.5%, p<0.0001) frequency-current slope, and an increased incidence of persistent inward current. Because basic properties became more diverse in old motoneurons and the slope of the frequency-current relationship, which is normally similar for high and low threshold motoneurons, was lower in the old group, we conclude that aging alters the biophysical properties of motoneurons in a fashion that cannot be simply attributed to a loss of high-threshold motoneurons. Surprisingly, caloric restriction, which is known to attenuate aging-associated changes in hindlimb muscles, had no effect on the progress of aging in the innervating motoneurons.