Aging is associated with an altered ability to match oxygen delivery (QO₂) to consumption (VO₂) in skeletal muscle and differences in the temporal profile of vasodilation may provide a mechanistic basis for the QO₂-to-VO₂ mismatching during the rest-to-exercise transition. Therefore, we tested the hypothesis that the speed of vasodilation will be blunted in skeletal muscle first-order arterioles from old versus young rats. Arterioles from the soleus and the red portion of the gastrocnemius (Gast_Red) muscles were isolated from young (Y, 6 mo; n=9) and old (O, 24 mo; n=9) Fischer-344 rats and studied in vitro. Vessels were exposed to acetylcholine (ACh; 10^-6 M), sodium nitroprusside (SNP; 10^-4 M) and increased intraluminal flow and the subsequent vasodilation was recorded at 30 frames/s. The data was fit to a monoexponential model and the dynamics of vasodilation (i.e., time delay, time constant (tau) and rate of change (delta/tau)) were calculated. With old age, the rate of vasodilation was significantly blunted in resistance vessels from the soleus to ACh (Y, 27.9 ± 3.6; O, 8.8 ± 2.6 μm/s) and flow (Y, 12.8 ± 2.1; O, 3.1 ± 0.9 μm/s). In the Gast_Red the old age-associated impairment of endothelium-dependent vasodilator dynamics was even greater than that of the soleus. With SNP neither the magnitude nor time constant of vasodilation were affected by age in either muscle. The results indicate that aging impairs the dynamics of vasodilation in resistance vessels from the soleus and Gast_Red muscles mediated, in part, through the endothelium. Thus, the old age-associated slower rate and magnitude of vasodilation could inhibit the delivery of O₂ during the critical transition from rest-to exercise in moderate to highly oxidative skeletal muscle.