This study used optical coherence tomography (OCT) to evaluate morphologic changes in vasospastic lesions, which can cause acute coronary syndrome (ACS) or chronic stable VA. Thirty-nine patients (52.4 ± 9.0 years, 33 males) with vasospasm-induced ACS who presented with chest pain and displayed transient ST segment elevation on electrocardiography were included in the ACS group. Forty-one patients (49.3 ± 7.7 years, 33 males) who presented with chronic stable variant angina were included in the VA group. The clinical characteristics and morphologic OCT results of the two groups were compared. There were no differences in baseline characteristics, including the proportions of hypertension, diabetes mellitus, and smoking, between the two groups. Intimal tear, erosion, and intra-luminal thrombi were more frequent in the ACS group than the VA group (P < 0.001, P < 0.001, and P = 0.006, respectively). High-sensitivity C-reactive protein level was higher in the ACS group than the VA group (1.33 ± 1.93 vs 0.48 ± 0.50 mg/l, P = 0.011). Maximal intima thickness of spastic segment (0.38 ± 0.06 vs 0.31 ± 0.05 mm, P < 0.001) was significantly greater in the ACS group than in the VA group. In patients with vasospasm-induced ACS, intimal tear, intimal erosion, and microthrombi are major abnormal morphologic findings of OCT compared with patients with chronic stable VA.