The relationship between suicide and rumination in depression is a recent topic of attention in mental health. The purpose of this study was to investigate the relationship between demographic variables, depressive symptoms, rumination, and suicide ideation in patients with depression, as well as the predictors of suicide ideation. Research design: A cross-sectional study of 95 subjects with depression recruited intentionally from the psychiatric ward of Tzu Chi Hospital. The questionnaire included demographic data, the Beck Depression Inventory-II, the Ruminative Response Scale, and the Beck Scale for Suicide Ideation. Independent sample t-test, Pearson product difference correlation, and the stepwise regression test were adopted for data analysis. Results: Age (r = −0.41, p < 0.01), age at diagnosis (r = −0.34, p < 0.01), and sleep duration (r = −0.25, p < 0.05) were negatively correlated with rumination–reflection. The depressive symptoms (r = 0.72, p < 0.01) were positively correlated with rumination, whereas rumination (r = 0.57, p < 0.01) and suicide ideation were positively correlated. Depressive symptoms and rumination could predict suicide ideation, and the effective explanatory power reached 60%. Conclusions: If the patient with depression was younger or the patient was diagnosed at a younger age, the depressive symptoms of the reflection subscale of rumination thinking and suicide ideation were more serious. Our results indicate that clinicians who care for patients with depression should be aware of rumination and its impact on suicide ideation, specifically in younger patients.