Beliefs regarding the controllability and usefulness of positive and negative emotions are fundamental factors influencing emotion regulation and mental health. Given the scarcity of assessment tools in this domain, the present study aimed to evaluate the psychometric properties of the Emotional Beliefs Questionnaire and examine the relationship between these beliefs, emotion regulation, and symptoms of affective disorders. This study was conducted on 388 young adults aged 18 to 35 in Zanjan. To evaluate the technical properties of the instrument, qualitative and quantitative content validity indices, Confirmatory Factor Analysis, and Pearson correlation for convergent validity were employed, alongside Cronbach’s alpha and test-retest reliability assessments. Results of the Confirmatory Factor Analysis showed that this questionnaire possesses a four-factor structure comprising negative controllability, positive controllability, negative usefulness, and positive usefulness. Cronbach’s alpha coefficients for positive control 0.74, negative control 0.79, positive usefulness 0.73, and negative usefulness 0.71 indicated desirable internal consistency. Furthermore, a one-week test-retest reliability coefficient of 0.71 confirmed the scale’s temporal stability. Content validity indices for all items were reported above 0.80. In terms of convergent validity, significant correlations were observed between emotional beliefs and depression 0.17, anxiety 0.22, and stress 0.15. The Emotional Beliefs Questionnaire demonstrates strong psychometric properties within the Iranian population. Despite limitations in generalizability due to specific sample characteristics, this instrument can serve as a valid scale in clinical research and the design of therapeutic interventions to assess emotional beliefs and promote community mental health.