The present study aimed to investigate psychopathology resulting from cancer diagnosis, emphasizing the mediating role of mentalization in the relationship between personality dimensions and clinical disorders, in the cancer patient community of Urmia city. The present study was descriptive-correlational and was conducted within the framework of a clinical research on 170 cancer patients referring to Urmia medical centers in 1403. Data collection tools included the Big Five Personality Factors Questionnaire (NEO-FFI), Mentalization Scale (RFQ), and Clinical Symptom Checklist (SCL-90-R). The data were analyzed using descriptive statistical methods, Pearson correlation, independent t-test, and structural equation modeling (SEM). The results showed that neuroticism had the highest positive correlation with mental disorders (r=0.64, p<0.001) and mentalization had a negative and significant correlation with psychopathology (r=-0.53, p<0.001). Also, patients with high mentalization experienced lower levels of psychopathology. In structural equation modeling, the mediating role of mentalization in the relationship between neuroticism and mental disorders was confirmed (indirect effect β=0.12, p<0.01) and the model fit indices (CFI=0.94, RMSEA=0.06) were assessed as appropriate. Overall, the findings of this study indicate that personality traits and patients' mentalization capacity have a significant effect on psychopathology resulting from a cancer diagnosis.