To preliminarily evaluate the safety and efficacy of the WeFlow-JAAA endograft, a novel off-the-shelf device designed for the repair of juxtarenal abdominal aortic aneurysms (JRAAAs) and pararenal abdominal aortic aneurysms (PRAAAs). This prospective single-arm first-in-human clinical trial included patients with JRAAAs (infrarenal necks ≤10 mm) or PRAAAs with at least a 5 mm sealing zone below the superior mesenteric artery (SMA) who underwent endovascular repair using the WeFlow-JAAA endograft system. With this system, the celiac artery was addressed with a wide scallop, the renal arteries (RAs) were addressed with 2 standard inner branches, and the SMA was addressed with a "mini-inner-cuff" reinforced fenestration. The primary efficacy endpoint was the clinical success at 12 months. The primary safety endpoint was the freedom from major adverse events (MAEs) in the first 30 days after surgery. Fifteen patients (all men; mean age 68.5±6.0 years) were enrolled between October 2019 and August 2021. The median infrarenal neck length was 0 mm (IQR, 0-4 mm). Technical success was achieved in all patients. No MAEs occurred in the first 30 days. The mean fluoroscopy time was 73.1±27.8 minutes, and the mean volume of contrast media was 130.7±29.4 mL. Clinical success was maintained in all patients at 12 months. No aortic-related deaths, aneurysm rupture, type I or type III endoleak, or open surgery conversion occurred during the follow-up period. The secondary intervention was required only in 1 patient who developed an occluded right RA stent 14 months after the procedure. The WeFlow-JAAA endograft device appears to be safe and efficacious in selected patients with JRAAAs or PRAAAs with more than 5 mm sealing zone below SMA. Large-scale, multicenter, and prospective studies with long-term follow-ups are ongoing to validate our findings in China. Clinicaltrials.gov identifier: NCT04745546 (URL: Guo's Visceral Arteries Reconstruction: The First in Man Study of WeFlow-JAAA Stent Graft System-Full-Text View-ClinicalTrials.gov). The first-in-human clinical trial of the WeFlow-JAAA endograft system demonstrates promising safety and efficacy in treating juxtarenal abdominal aortic aneurysms (JRAAAs) and partial pararenal abdominal aortic aneurysms (PRAAAs). This innovative off-the-shelf device offers a potential alternative to traditional endovascular aortic repair. The successful outcomes, including technical success in all patients, freedom from major adverse events, and maintenance of clinical success at 12 months, suggest a potential shift in clinical practice towards using the WeFlow-JAAA endograft system for selected patients. This study paves the way for larger-scale, multicenter, prospective studies to further validate its long-term safety and efficacy, offering clinicians a new option for managing complex abdominal aortic aneurysms.