BACKGROUND: Evidence suggests that poor mental health (MH) is a risk factor for the health of older adults. Dietary diversity is considered to be related to healthy aging. However, the relationship between diet and MH is still unclear. Therefore, the purpose of this study was to investigate the relationship between dietary diversity score (DDS) and anxiety and depression among centenarians and their offspring and spouses. METHODS: Our study was observational and cross-sectional. The Generalized Anxiety Disorder Scale (GAD-7), the 15-item version of the Geriatric Depression Scale (GDS-15), and the dietary frequency questionnaire were used to measure the status of anxiety, depression, and dietary diversity. Data were analyzed by Student's t-test, χ2 test, Mann-Whitney U test, correlational analysis, and univariate or multivariate logistic regression. RESULTS: Among the 288 older adults, 12.8% reported symptoms of depression, and 8.7% reported anxiety. People with a lower dietary diversity had higher rates of anxiety and depression. After controlling for age, place of residence, economic status, alcohol drinking, and physical activity, a lower DDS was found to be a risk factor for depressive symptoms [odds ratio (OR): 2.237; 95% confidence interval (CI): 1.009-4.959; P=0.048]. DDS was negatively correlated with depression score in older adults (r=-0.224; P<0.001), especially offspring and their spouses (r=-0.275; P<0.001). However, no significant relationship was observed between DDS and anxiety. In addition, eating legumes (OR: 0.415; 95% CI: 0.188-0.920; P=0.030) and nuts (OR: 0.255; 95% CI: 0.116-0.561; P=0.001) at least once a week can act as protective factors for depression. Eating nuts (OR: 0.405; 95% CI: 0.168-0.978; P=0.044) and meat (OR: 0.396, 95% CI: 0.161-0.975; P=0.044) at least once a week can act as protective factors for anxiety. CONCLUSIONS: These results suggest an association between low dietary diversity and a higher incidence of mental disorders. Further, the possibility of reverse causality cannot be ruled out. It is necessary to conduct further prospective studies.