Although the psychological denial model argues that poor insight is a result of defense mechanisms, the direct relationship between the two remains unclear. This study aimed to examine the relationship between insight into illness and defense mechanisms while considering cognitive dysfunction in schizophrenia. A total of 38 patients with schizophrenia were evaluated for level of insight (Schedule for the Assessment of Insight), defense mechanisms (Defense Style Questionnaire), neurocognitive function (Brief Assessment of Cognition in Schizophrenia), and psychotic symptoms (Brief Psychiatric Rating Scale). Regarding level of insight, partial correlation analysis controlling neurocognitive and psychotic variables showed that "recognition of illness" was positively correlated with immature defense styles and negatively correlated with mature defense styles. Stepwise regression analyses revealed that "recognition of illness" was significantly predicted by immature defense styles. Our findings suggest that patients who tend to use immature defense styles are more likely to accept their own mental illness.