Blood glucose variability is considered to be one of the risk factors for coronary heart disease, and there is growing evidence that blood glucose fluctuation is closely related to the characteristics of plaques. The aim of the study was to investigate the influence of blood glucose variability on the vulnerability of culprit plaques in elderly non-ST segment elevation acute coronary syndrome (NSTE-ACS) patients. Coronary angiography and VH-IVUS were applied to evaluate the components of culprit plaque in NSTE-ACS patients. CGMS monitoring was performed for 72 hours and blood glucose variability was assessed by glycemic excursions (MAGE), absolute means of daily differences (MODD), postprandial glycemic excursions (PPGE), and the largest amplitude of glycemic excursions (LAGE). An oxidative stress indicator (urinary 8-iso-PGF(2 alpha)) was also tested. Eighty two elderly NSTE-ACS patients were enrolled in this study. Higher glucose variability was associated with the increased culprit plaque instability. MODD was positively correlated with urinary 8-iso-PGF(2 alpha). PPGE and urinary 8-iso-PGF(2 alpha) were independent risk factors for percent fibrous and necrotic volume in culprit plaques (PPGE: beta = -0.340, P = 0.024; urinary 8-iso-PGF(2 alpha): beta = -0.294, P = 0.013). Blood glucose variability is positively related to oxidative stress. With an increase in blood glucose variability, the instability of criminal plaques in elderly NSTE-ACS patients increased.