BACKGROUND: The treatment course for depression is multifactorial, and the gold standard method for antidepressant selection remains unclear. Therefore, we focused on patients' personality as a possible indicator of the treatment response to mirtazapine and selective serotonin reuptake inhibitors (SSRIs) and whether it can contribute to antidepressant selection. METHODS: One hundred one patients with major depressive disorder were randomized at baseline to receive either mirtazapine or SSRI treatment. Their personality was measured using the NEO Five-Factor Inventory at baseline, and depressive symptoms were evaluated using the Hamilton Rating Scale for Depression at baseline and 4 and 8 weeks. Stepwise multivariable logistic regression and receiver operating characteristic analyses were performed to determine the association of personality traits with remission and better antidepressant selection. RESULTS: Neuroticism had the substantial influence on remission at 4 and 8 weeks among the entire sample. The cutoff T-score of neuroticism for predicting remission at 4 weeks was 62.5. The patients with moderate neuroticism (scores below the cutoff) were more likely to experience remission after 4-week mirtazapine treatment (remission rate: 73.7 %) than after SSRI treatment (40.0 %); those with high neuroticism (scores above the cutoff) were more likely to experience remission after 8-week SSRI treatment (74.1 %) than after mirtazapine treatment (35.7 %). LIMITATIONS: The small sample size increased the confidence intervals. CONCLUSIONS: The treatment response of the patients with depression differed according to the type of antidepressants and degree of neuroticism. Measuring personality traits at treatment initiation may help in selecting better antidepressants and predicting the time to remission.