The symptoms of borderline personality disorder (BPD) are often observed in young adults. They have difficulty in adaptation. Therefore, it is important to assess the extent of their BPD symptoms to ascertain intervention. However, there is no scale to assess BPD symptoms and their changes in young adults in Japan. Therefore, we developed a Japanese version of the Quick Evaluation of Severity over Time (QuEST-J) to assess these symptoms and investigated the reliability and validity of this scale in a sample of Japanese undergraduates ( N ＝733). QuEST-J comprises three sub-scales: “Thoughts and Feelings,” “Behaviors-Negative,” and “Behaviors-Positive.” A confirmatory factor analysis corroborates the factorial validity. Moreover, the results indicate enough internal consistency, test-retest reliability, and criterion-related validity. Therefore, QuEST-J is a reliable and valid scale to assess BPD symptoms in young adults.