The purpose of this study is to present a diagnostic evaluation tool that can more accurately determine the academic performance level in Korean language proficiency of foreign undergraduate students studying at domestic universities. The diagnostic evaluation diagnoses the academic Korean language proficiency of foreign undergraduates, and provides the diagnosis results to foreign undergraduates, professors, and university institutions so that teaching activities can be conducted efficiently. In this study, it was considered that the ‘Basic Academic Ability Diagnostic Test for the Korean Language Subject' was suitable as a test tool for diagnosing to diagnose the academic achievment of foreign undergraduates. This diagnostic test is a diagnostic tool designed for Korean students in Korea, and it not only continuously verifies its reliability and validity, but also includes background knowledge that Korean university students in Korea are basically acquiring. To prove that the 'Basic Academic Ability Diagnostic Test' is suitable as a diagnostic evaluation tool for foreign undergraduates, the correlation with the Korean language achievement evaluation was analyzed. The correlation between diagnostic evaluation and other items showed a significantly positive correlation. When the diagnostic evaluation score was good, the pre-test and post-test scores of Korean language proficiency, and the TOPIC level was also high. This result proves that the basic academic ability diagnostic test tool is very suitable as a diagnostic evaluation tool for foreign undergraduate students. Also, the analysis result of the pre- and post-tests and the TOPIK test showed a very significant and strong positive correlation with the post-test, and the higher the TOPIK grade, the higher the score of the pre‐test.