The roles of interleukin-10 (IL-10) have been emphasized in several models of glomerulonephritis (GN). Three biallelic polymorphisms within the IL-10 promoter region, at positions -1,082, -819, and -592 from the transcription initiation site, were shown to affect the level of IL-10 production. To investigate the effect of IL-10 promoter polymorphisms on the predisposition to development of GN in Korea, IL-10 promoter polymorphisms were assayed by polymerase chain reaction followed by restriction fragment length polymorphism in 108 patients with IgA nephropathy (IgAN), 49 focal segmental glomerulosclerosis (FSGS), and 100 healthy controls. In comparison with the control, the frequency of -1,082*G alleles were lower in IgAN and the frequencies of -592*C and -819*C were lower in FSGS, respectively. As for the haplotype, GCC haplotype was less frequent among IgAN than the control and ATA haplotype was more frequent among FSGS than the control (p < 0.05). The frequency of intermediate producer genotypes (GCC/ACC and GCC/ATA) were lower among IgAN or FSGS than the control. Our findings suggested that IL-10 promoter polymorphism predisposed to the development of IgAN and FSGS in Korean patients.