BACKGROUND: Affective temperament and emotional expression can be important in the mental and physical consequences of patients with cancer. This study aimed to determine the role of affective temperament and emotional expression in predicting CHRONIC FATIGUE in patients with cancer. METHODS: 110 patients with cancer, hospitalized in the surgery and hematology wards of Fatemi and Imam Khomeini Hospitals in Ardabil City, Iran, in autumn of 2016, were selected by purposive sampling and participated in this cross-sectional study. The Affective and Emotional Composite Temperament Scale (AFECTS), Berkeley Expressivity Questionnaire (BEQ), and Chalder FATIGUE Scale (CFQ) were used to collect data. The collected data were analyzed by correlation coefficient and multiple regression analysis using SPSS software. RESULTS: CHRONIC FATIGUE positively correlated with depressive (r = 0. 69, P < 0. 01), anxious (r = 0. 59, P < 0. 01), apathetic (r = 0. 64, P < 0. 01), dysphoric (r = 0. 37, P < 0. 01), volatile (r = 0. 61, P < 0. 01), irritable (r = 0. 36, P < 0. 01), disinhibited (r = 0. 33, P < 0. 01), and obsessive (r = 0. 52, P < 0. 01) affective temperaments, but it negatively correlated with cyclothymic (r =-0. 35, P < 0. 01), hyperthymic (r =-0. 62, P < 0. 01), euphoric (r =-0. 69, P < 0. 01), and euthymic (r =-0. 21, P < 0. 01) affective temperaments. Also, it was found that there was a negative relationship between CHRONIC FATIGUE and emotional expression (r =-0. 27, P < 0. 01). Results of regression analysis showed that 79% of the total variance of CHRONIC FATIGUE was explained by affective temperaments. In addition, 27% of the total variance of the CHRONIC FATIGUE was explained by emotional expressiveness. CONCLUSION: These findings suggest that we can consider the affective temperament and emotional expression as psychological factors underlying the CHRONIC FATIGUE in patients with cancer.