Aims: To investigate the genetic polymorphism of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) in children with idiopathic nephrotic syndrome (INS), as well as its relationship with patient’s clinical response to steroid therapy. Methods: Fifty-nine patients with INS were recruited and divided into 2 groups according to their clinical response to steroids: steroid-sensitive (SS) with 19 patients and non-SS with 40 patients, which was further divided into steroid-dependent (SD) and steroid-resistant (SR) groups with 35 and 5 patients, respectively. Seventy-nine children without previous renal diseases and negative proteinuria were enrolled as a control group. The genotypes for ACE I/D polymorphism, including DD, ID, and II, were analyzed. Results: The distribution of ACE DD, ID, and II genotypes in INS patients were 52.5, 10.2 and 37.3%, respectively; the corresponding numbers for the control group were 2.5, 25.3 and 72.2%, respectively. Patients with INS had a significantly higher percentage of DD genotype (p <0.001) than the control group. This higher incidence of the DD genotype was observed in both the SS and non-SS groups. A higher percentage of the DD genotype in the non-SS group and in the SD group as compared to the SS group (both p < 0.05) was also noted. Conclusion: Our data shows that INS is associated with a higher incidence of the DD genotype, especially in non-SS patients. This finding suggests that the DD genotype may be a risk factor for INS and play a role in the clinical response to steroids.