The aim of this study was to investigate the association between bone mineral density (BMD) and coronary artery calcification (CAC) in adults with osteopenia or osteoporosis. A retrospective medical review study was conducted in a regional hospital in southern Taiwan. Medical records of patients who underwent both a coronary computed tomography scan and a BMD measurement were identified. Multinomial logistic regression analyses were used to assess the association between BMD and CAC levels in patients with osteopenia or osteoporosis. Of the 246 patients, 119 were female and 42.3% had CAC. For patients with osteopenia, after adjusting for the significant factors of CAC, no significant association was observed between BMD with either moderate CAC (0 < CAC score ≤ 100) or high CAC (CAC score > 100). However, in patients with osteoporosis, after adjusting for the significant factors of CAC, BMD in the lumbar spine was inversely associated with moderate CAC (odds ratio = 0.38, p = 0.035). In conclusion, a lower BMD in the lumbar spine was associated with an increased risk of moderate CAC in patients with osteoporosis. It is crucial to take action to maintain bone health, particularly in those who already have osteoporosis, to reduce the risk of developing CAC and its associated morbidity and mortality.