Neuroradiologists and neurosurgeons, who are interested in noninvasive imaging biomarkers for predicting grades of adult diffuse gliomas.To investigate the diagnostic value of APT compared with those of ADC and rCBV, and incremental diagnostic value of APT over ADC and rCBV for predicting histopathological grade in diffuse gliomas in adults, with clinically optimized APT imaging protocols.The study cohort consisted of 39 adult patients with histopathologically proven diffuse glioma who underwent preoperative APT imaging, with 34 patients available for preoperative DSC MRI and DWI. Regions of interest were obtained from circles manually placed at the area with high signal in APT and rCBV map, and low signal in ADC map. APT signal was compared according to WHO grade or low vs high grade of glioma. Diagnostic ability to discriminate high grade glioma from low grade glioma were compared between APT, ADC, and rCBV by using Receiver operative characteristic (ROC) analysis, and incremental diagnostic value of APT over ADC and rCBV were assessed by using integrated discrimination index. Also, the correlation between APT values and Ki-67 labeling index (LI) was assessed by linear regression.The APT SI values were 0.82 ± 0.36% in grade II gliomas, 1.73 ± 0.86% in grade III, and 2.62 ± 0.78% in grade IV gliomas, which showed significant difference between grade II and III (p=0.018), III and IV (p = 0.010), as well as II and IV (p < 0.001). The diagnostic value to discriminate between high and low grade glioma was not significantly different between APT, ADC and rCBV, with area under the ROC curve (AUC) of 0.890, 0.917, and 0.947, respectively. (p > 0.05 for each comparison) Incremental diagnostic value of APT was significant over ADC (p = 0.003), and not significant over rCBV (p=0.066). APT signals were significantly correlated with Ki-67 LI. (p=0.001, R-squared = 0.26)APT imaging, a subtype of CEST, can indirectly provide information about peptide or protein concentration within the tissue and has been investigated as an imaging biomarker in previous studies. However, these previous studies have limited clinical feasibility, since APT imaging protocol was not optimized for clinical use, mouse models instead of human were scanned using experimental MRI with 4.7T or higher magnetic field, and human patients were scanned in only one representative slice of tumor. Herein, we optimized the APT imaging protocol using 3T MRI in clinic and validated APT imaging clinically in glioma patients, and showed that APT imaging has incremental diagnostic values over ADC values for glioma grading.APT imaging can be useful, and have incremental value over ADC for predicting the histopathological grades of adult diffuse gliomas. APT SI can be correlated with Ki-67 LI.