Objective This study aimed to investigate whether ultrasound parameters during non-painful episodes could indicate impaired differential renal function (DRF) in patients with ureteropelvic junction obstruction (UPJO) and intermittent abdominal pain. Methods We conducted a retrospective review of all cases of unilateral UPJO with intermittent abdominal pain undergoing their first pyeloplasty between March 2019 and October 2021. Clinical characteristics, such as gender, affected side, age at the first onset of pain, waiting time for pyeloplasty, age, and concurrent symptoms, were collected. Ultrasound examination (US) was used to measure the anteroposterior diameter (APD) and renal parenchyma thickness (PT) during intermittent pain episodes and dynamic renal scintigraphy (RDS) was used to assess DRF. Results This study investigated the characteristics and demographics of 109 patients with UPJO. Of the patients, 28.4% had baseline DRF less than 40%, and factors affecting baseline DRF were analyzed. Patients diagnosed with hydronephrosis before the onset of pain had a lower risk of DRF impairment compared to those diagnosed after the onset of pain (p = 0.021). Patients with impaired renal function had larger APD and thinner PT values on ultrasound (p = 0.002, p༜0.001). Abdominal pain accompanying symptoms were found to be associated with DRF impairment (p = 0.044). Multifactorial analysis identified that right UPJO, diagnosis of UPJO after pain onset, large APD, and thin PT were risk factors for baseline DRF damage in patients with intermittent abdominal pain (p༜0.05). Conclusion Patients with right-sided UPJO, UPJO diagnosed after a pain episode, and those with larger APD and thinner PT on ultrasound during pain-free intervals were more likely to have DRF impairment.