Objective　To investigate the effect of immune cell from idiopathic nephrotic children on extracellular matrix (ECM) synthesis by cultured rat glomerular epithelial cell (GEC) and on the proliferation of mesangial cell (GMC). Methods　Twenty-eight children with idiopathic nephrotic syndrome and 15 age-matched healthy children were randomly selected and divided into 4 groups: Group 1, untreated nephrotic children; Group 2, glucocorticoid treated nephrotic children; Group 3, children undergoing glucocorticoid treatment with negative proteinuria; and Group 4, normal control. The peripheral blood mononuclear cells (PBMC) were collected from these children and PBMC conditioned medium (PBMC-CM) were prepared. The PBMC-CM was co-cultured with GEC and GMC respectively. The concentrations of collagen, laminin, collagen Ⅲ and collagen Ⅳ in the GEC and PBMC-CM co-culture medium were investigated. The GMC proliferation was measured by the 3　H-thymidin incorporation method. Results　The 3 H-proline incorporation coefficients of the GEC treated with the PBMC-CM of the 4 groups were 0.93, 1.24, 1.23, and 1.11, respectively. The laminin inhibitory coefficients of the 4 groups were 0.95, 1.02, 1.01, and 1.04, respectively. The inhibitory coefficients of collagen Ⅲ were 0.97, 1.00, 0.99, and 1.01, respectively, for the 4 groups. All these parameters showed a significant difference between Group 1 and the other 3 groups (P<0.05). However, there was no significant difference in the inhibitory coefficient of collagen Ⅳ between each two of the 4 groups (1.04, 1.05, 1.04, 1.08, P>0.05). The 3　H-thymidine incorporation coefficients of GMC responsive to PBMC-CM were 1.21, 1.53, 1.50, and 1.10, respectively, and no significant difference was found between the 4 groups (P>0.05). Conclusion　The results suggested that the circulating immune cells from idiopathic nephrotic children have a direct effect on some ECM component synthesis in cultured rat GEC; the bio-activity of immune cells could be neutralized by administering glucocorticoid; and the circulating immune cells of nephrotic children have no direct effect on GMC proliferation.