Abstract: Disclosed is a prostate cancer diagnostic biomarker composition including, as an active ingredient, at least one kynurenine pathway metabolite selected from kynurenine and anthranilate. Also disclosed are a prostate cancer diagnostic composition including an agent capable of measuring the level of the biomarker and a prostate cancer diagnostic kit including the prostate cancer diagnostic composition. The use of the prostate cancer diagnostic biomarker composition can significantly improve the accuracy of prostate cancer diagnosis as an alternative or supplement to the use of PSA levels for prostate cancer diagnosis according to the prior art, which has difficulty in ensuring accurate diagnosis. Therefore, the biomarker composition can be widely used in a variety of industrial applications, including medical applications.