Idiopathic nephrotic syndrome (INS) is characterized by marked urinary excretion of albumin and other intermediate-sized plasma proteins, such as transferrin and vitamin D-binding protein. Some cases even develop anemia. The aim of this study was to investigate the changes in serum iron, transferrin, and erythropoietin, and the relationships between serum and urine transferrin and erythropoietin. Thirty-seven children with INS and 35 age- and sex-matched healthy children were investigated. The indexes related to iron metabolism, including serum iron, ferritin, transferrin, total iron-binding capacity (TIBC), transferrin saturation, and hematological parameters [hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH)], and urinary transferrin and erythropoietin were measured in 37 children with INS before treatment and at the remission stage. Thirty-five age- and sex-matched healthy children served as controls. Serum iron levels (18.8 ± 3.8) ?mol/L in INS patients before treatment were significantly lower than those of the healthy controls (22.2 ± 3.8) ?mol/L and those measured at the remission stage (21.0 ± 3.5) ?mol/L (all < 001). Serum transferrin levels in INS patients before therapy (1.9 ± 0.3) g/L also decreased compared with the healthy controls (3.1 ± 0.5) g/L and the measures at the remission stage (2.9 ± 0.6) g/L (all < 0.01). In contrast, serum TIBC and transferrin saturation were significantly higher in INS patients before treatment than in the healthy controls [TIBC (56.4 ± 9.2) ?mol/L (50.7 ± 6.8) ?mol/L, < 0.01; transferrin saturation (55.7±9.2)% (46.4 ± 8.2)%, < 0.01] and they were also higher than the measures at remission stage [(51.9 ± 7.7) ?mol/L and (47.4 ± 13.3) ?mol/L] (all < 0.01). Serum transferrin was positively correlated with serum albumin ( = 0.609, < 0.01) and negatively correlated with urinary transferrin ( = -0.550, < 0.01) in INS patients before treatment. We conclude that serum iron, transferrin and erythropoietin levels are markedly decreased in INS patients, which may be partially related to the urinary loss of these indexes.