Purpose: The purpose of this study was to determine the factors that affect suicidal ideation in patients with chronic mental illnesses, such as schizophrenia, depressive disorder, and bipolar disorder. Methods: The research participants were 160 patients with mental illnesses residing in B City and G Province. They responded to questionnaires about their suicidal ideation, self-esteem, depression, family support, social support, and internalized stigma of mental illness. The collected data were analyzed using t-test, ANOVA, Pearson correlation coefficients, and STEPWISE multiple regression with the SPSS/WIN 18.0 program. Results: History of self-esteem, Depression, Social support, Psychiatric diagnosis of MDD and suicide attempt showed an explanatory power for 64% of suicidal ideation in patients with chronic mental illnesses. Conclusion: Specialized health and medical service personnel providing services to patients with chronic mental illnesses must determine the risk factors and protective factors for suicidal ideation associated with each illness, and establish a more individualized and systemized case management system based on customized approach.