Recently, blood oxygenation level-dependent (BOLD) MRI has been utilized to investigate cerebrovascular response induced by hypercapnia challenges. There are alterations in cerebrovascular system during normal aging, which may result into difference in hemodynamic response between young and old adults. This study was aimed to evaluate the aging effects on BOLD response to breath holding by using a 3-Tesla clinical MRI system. There were 12 healthy old adults (F/M=10/2, 61-78 y/o) and 20 healthy young adults (F/M=8/12, 20-31 y/o) recruited for this study. The breath-hold paradigm comprised of one 30-second preparation stage (natural breathing) and three 60-second periodic breath-hold cycles (holding breath for 15 seconds and natural breathing for 45 seconds). BOLD MRI was performed using a T2*-weighted single-shot gradient echo echo-planar imaging (TR/TE/FA=3000 msec/35 msec/90°, matrix size=64 x 64, in-plane resolution=3 mm x 3 mm). The change of end-tidal CO_2 (ΔEt CO_2 in mmHg) was measured for each subject. There were three major findings in this study. First, the activation volume during breath holding was significantly smaller in the old group (983.4 ± 380.2 cm^3) than in the young group (1270.1 ± 447.8 cm^3) (p=0.04). Second, there was lower, but not significant, average BOLD signal change in the old group (1.26 ± 0.24 %) as compared with the young group (1.48 ± 0.59 %). Third, cerebrovascular reactivity (CVR), in terms of %BOLD signal change/ΔEtCO_2, was significantly lower in the old group (0.14 ± 0.04 %/mmHg) than in the young group (0.20 ± 0.10 %/mmHg) (p=0.02). The present study demonstrated that there were significant aging effects causing lower cerebrovascular response to hypercapnia stress, which should be taken into account for when applying BOLD MRI for clinical study.