Impaired glucose metabolism is associated with an increased risk of cardiovascular complications, and coronary artery spasm is thought to underlie the development of coronary artery disease. Intraday glucose variability (GV) accelerates oxidative stress and inflammatory cytokine release, but its impact on coronary artery spasm remains unclear. This study investigated the relationship between intraday GV and coronary artery spasm. The study included 50 patients with dysglycemia and suspected coronary spastic angina. GV was analyzed by 24-h monitoring of the blood glucose concentration using a flash glucose monitoring system. The mean amplitude of glycemic excursion (MAGE) was calculated as an index of GV. Coronary artery spasm was assessed using the intracoronary acetylcholine provocation test. Coronary spasm was defined as acetylcholine-induced total or subtotal coronary occlusion. Changes in vessel diameter in response to acetylcholine were evaluated with quantitative coronary angiography. Coronary artery spasms were observed in 21 patients (42%). MAGE was significantly higher in patients with spasms compared to those without spasms (127.5 ± 33.5 vs. 91.4 ± 37.6, p < 0.01). Regression analysis showed a positive correlation between MAGE levels and coronary diameter changes induced by acetylcholine (r = 0.47, p < 0.01). In multiple regression analysis, MAGE was independently associated with acetylcholine-induced coronary diameter change (β = 0.47, p < 0.01). Intraday GV was associated with coronary artery spasm in patients with dysglycemia.