During spinal anesthesia for cesarean section, cerebral oxygenation decreases may be related to an abrupt drop in cerebral blood flow due to hypotension. We measured the changes in maternal regional cerebral blood volume (rCBV) and oxygenation (rCBO) using near-infrared spectroscopy (NIRS) to evaluate whether a decrease in arterial blood pressure during spinal anesthesia diminishes rCBV and rCBO. Forty patients scheduled for elective cesarean section under spinal anesthesia were monitored for mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), and concentrations of oxy-hemoglobin (Hb), deoxy-Hb, total-Hb, and tissue oxygenation index (TOI), before spinal anesthesia (baseline) and for 20 min after intrathecal injection of bupivacaine. We investigated changes in the values from baseline and evaluated whether the maximum changes in total-Hb (Δ-total-Hb) and TOI (Δ-TOI) correlate with changes in MAP at the same time point. The mean oxy-Hb, total-Hb, TOI, and MAP significantly decreased from baseline after intrathecal injection of bupivacaine (P < 0.01). There were significant positive correlations between both Δ-total-Hb and Δ-TOI and the decrease in MAP (Δ-total-Hb: r = 0.53, P < 0.01; Δ-TOI: r = 0.59, P < 0.01). Maternal rCBV and rCBO decrease significantly during spinal anesthesia for cesarean section. Reductions in rCBV and rCBO may be associated with the severity of hypotension induced by subarachnoid sympathetic block with bupivacaine.