We have recently found that indoxyl sulfate induces prorenin expression in proximal tubular cells. The present study aimed to determine whether nuclear factor-κB (NF-κB) p65, signal transducer and activator of transcription 3 (Stat3), and reactive oxygen species are involved in indoxyl sulfate-induced prorenin expression in cultured human proximal tubular cells (HK-2 cells). Effects of indoxyl sulfate on prorenin expression were determined using HK-2 cells with small interfering RNAs (siRNAs) specific to NF-κB p65 and Stat3, N-acetylcysteine, an antioxidant, and diphenyleneiodonium, an inhibitor of nicotinamide adenine dinucleotide phosphate oxidase. Indoxyl sulfate increased prorenin expression in HK-2 cells. siRNAs specific to NF-κB p65 and Stat3 inhibited indoxyl sulfate-induced prorenin expression. Both N-acetylcysteine and diphenyleneiodonium suppressed indoxyl sulfate-induced prorenin expression. Indoxyl sulfate upregulates the expression of prorenin via NF-κB p65, Stat3, and reactive oxygen species in proximal tubular cells.