This study aimed to evaluate the renal blood flow (RBF) in patients with chronic kidney disease (CKD) using64Cu(II)-diacetyl-bis(4-methylthiosemicarbazonate) (64Cu-ATSM) for positron emission tomography (PET)/magnetic resonance imaging (MRI). We included five healthy controls (HCs) and ten patients with CKD. The estimated glomerular filtration rate (eGFR) was calculated from the serum creatinine (cr) and cystatin C (cys) levels. The estimated RBF (eRBF) was calculated using the eGFR, hematocrit, and filtration fraction. A single dose of64Cu-ATSM (300–400 MBq) was administered for RBF evaluation, and a 40 min dynamic PET scan was performed with simultaneous arterial spin labeling (ASL) imaging. PET-RBF images were obtained from the dynamic PET images at 3 min after injection using the image-derived input function method. The mean eRBF values calculated from various eGFR values differed significantly between the patients and HCs; both groups also differed significantly in terms of the RBF values (mL/min/100 g) measured using PET (151 ± 20 vs. 124 ± 22,p< 0.05) and ASL-MRI (172 ± 38 vs. 125 ± 30,p< 0.001). The ASL-MRI-RBF was positively correlated with the eRBFcr-cys (r = 0.858,p< 0.001). The PET-RBF was positively correlated with the eRBFcr-cys (r = 0.893,p< 0.001). The ASL-RBF was positively correlated with the PET-RBF (r = 0.849,p< 0.001).64Cu-ATSM PET/MRI demonstrated the reliability of PET-RBF and ASL-RBF by comparing them with eRBF. This is the first study to demonstrate that64Cu-ATSM-PET is useful for assessing the RBF and is well correlated with ASL-MRI.