Older adults suffering from mistreatment are especially vulnerable to adverse health outcomes. The current study examined the associations of elder mistreatment (single- and multi-type mistreatment) with depression or suicidal ideation in a Korean representative sample. The data were derived from the 2017 National Survey of Living Conditions and Welfare Needs of Korean Older Persons (unweighted n = 10,059 and weighted n = 10,055). Descriptive statistics and multivariate logistic regression analyses were performed. In the weighted population, 9.8% of older adults had mistreatment experiences. Results indicated that single- and multi-type mistreatment experiences were associated with increased risks of depression (OR = 1.93, 95% CI = [1.61, 2.32] and OR = 3.51, 95% CI = [2.52, 4.87], respectively), after adjusting for the confounding factors (socio-demographic, health-related, and social relation characteristics). Experiences of single- and multi-type mistreatment were also associated with suicidal ideation (OR = 2.48, 95% CI = [1.97, 3.12] and OR = 3.19, 95% CI = [2.25, 4.51], respectively), even after adjusting for the above confounding factors and depression. Similar results were found in sensitivity analyses using unweighted data. The current findings expanded our knowledge of the associations of mistreatment with depression and suicidal ideation in later life.