Purpose: This study reports Japanese normative data for the Unhelpful Thoughts and Beliefs about Stuttering (UTBAS) scales. We outline the translation process, and evaluate the psychometric properties of the Japanese version of the UTBAS scales. Methods: The translation of the UTBAS scales into Japanese (UTBAS-J) was completed using the standard forward-backward translation process, and was administered to 130 Japanese adults who stutter. To validate the UTBAS-J scales, scores for the Japanese and Australian cohorts were compared. Spearman correlations were conducted between the UTBAS-J and the Modified Erickson Communication Attitude scale (S-24), the self-assessment scale of speech (SA scale), and age. The test-retest reliability and internal consistency of the UTBAS-J were assessed. Independent t-tests were conducted to evaluate the differences in the UTBAS-J scales according to gender, speech treatment experience, and stuttering self-help group participation experience. Results: The UTBAS-J showed good test-retest reliability, high internal consistency, and moderate to high significant correlations with S-24 and SA scale. A weak correlation was found between the UTBAS-J scales with age. No significant relationships were found between UTBAS-J scores, gender and speech treatment experience. However, those who participated in the stuttering self-help group demonstrated lower UTBAS-J scores than those who did not. Conclusion: Given the current scarcity of clinical assessment tools for adults who stutter in Japan, the UTBAS-J holds promise as an assessment tool and outcome measure for use in clinical and research environments.