Abstract: Objective To study the clinical significance of transforming growth factor (TGF)-β1 and interleukin (IL)-18 mRNA in the diagnosis and evaluation of disease severity of primary nephrotic syndrome (PNS) in children. Methods The expression levels of TGF-β1 and IL-18 mRNA in peripheral blood mononuclear cells (PBMC) were measured by real-time fluorescent quantitative polymerase reaction (RT-PCR) in 77 children with PNS and 30 healthy children (control group). Results In children with steroid-sensitive nephrotic syndrome (SSNS), the expression levels of TGF-β1 and IL-18 mRNA before treatment and at 1, 4 weeks after hormone therapy were significantly lower in children with simple type nephrotic syndrome than those in children with nephritic type nephrotic syndrome (P<0.05). The level of TGF-β1 mRNA before treatment was significantly lower in children with SSNS than that in children with steroid-resistant nephrotic syndrome (SRNS). With the extension of hormone therapy, the expression levels of TGF-β1 mRNA showed a trend of declining in children with PNA. In children with SRNS, the expression levels of TGF-β1 and IL-18 mRNA before treatment and at 1, 4 weeks after hormone therapy were significantly lower in children with simple type NS than those in children with nephritic type nephrotic syndrome (P<0.05). In children with SSNS, the levels of TGF-β1 and IL-18 mRNA were significantly higher in acute phase than those in the remission phase. Conclusions At the early stage of PNS, the detection of the expression levels of TGF-β1 and IL-18 mRNA is useful for evaluatation of disease activity, clinical identification of nephritic type nephrotic syndrome and simple type nephrotic syndrome and early prediction of SRNS.