Background: IgA nephropathy (IgAN) is one of the most common primary glomerular diseases worldwide, but effective therapy remains limited and many patients progress to end-stage renal disease (ESRD). Only angiotensin-converting enzyme inhibitors (ACE-I)/angiotensin-receptor blockers (ARB) show a high level of evidence (1B level) of being of value in the treatment for IgAN according to the 2012 Kidney Disease: Improving Global Outcomes (KDIGO) guidelines. However, traditional Chinese medicine has raised attention in kidney disease research. Abelmoschus manihot, a single medicament of traditional Chinese medicine has shown therapeutic effects in primary glomerular disease according to the randomized controlled clinical trial that we have completed. Here, we conduct a new study to assess the efficacy and safety of Abelmoschus manihot in IgAN. Also, this study is currently the largest double-blind, randomized controlled registered clinical research for the treatment of IgAN. Methods: We will conduct a multicenter, prospective, double-blind, double-dummy randomized controlled study. The study is designed as a noninferiority clinical trial. Approximately 1600 biopsy-proven IgAN patients will be enrolled at 100 centers in China and followed up for as long as 48 weeks. IgAN patients will be randomized assigned to the Abelmoschus manihot group (in the form of a huangkui capsule, 2.5 g, three times per day) and the losartan potassium group (losartan potassium, 100 mg/d). The primary outcome is the change in 24-h proteinuria from baseline after 48 weeks of treatment. Change in estimated glomerular filtration rate (eGFR) from baseline after 48 weeks of treatment, the incidence of endpoint events (proteinuria >= 3.5 g/24 h, the doubling of serum creatinine, or receiving blood purification treatment) are the secondary outcomes. Twenty-four-hour proteinuria and eGFR are measured at 0, 4, 12, 24, 36 and 48 weeks. Discussion: This study will be of sufficient size and scope to evaluate the efficacy and safety of Abelmoschus manihot compared to losartan potassium in treating patients with IgAN. The results of this study may provide a new, effective and safe treatment strategy for IgAN.