Myeloid-related protein (MRP) 8 is a calcium-binding protein of the S100 family. The renal accumulation of macrophages expressing MRP8 is associated with the inflammatory activity of glomerulonephritis. We evaluated the renal accumulation of macrophages expressing MRP8 in children with IgA nephropathy (IgAN). We collected data on 25 IgAN children who had been treated with prednisolone and divided these patients into two groups: Favorable group, consisting of 11 patients with normal urine and 6 with minor urinary abnormalities at 4.3 ± 1.3 years after initial treatment; and Unfavorable group, consisting of 8 patients with persistent nephropathy. The pathological renal findings were compared between both groups. The second biopsy was performed at two years after first biopsy at 5.5 ± 4.9 months from onset. In Favorable group, the glomerular accumulation of macrophages expressing MRP8, and mesangial cells expressing α-smooth muscle actin (α-SMA) were lower in the second biopsy specimens than those of the first biopsy specimens. In Unfavorable group, the glomerular accumulation of macrophages expressing MRP8 detected in the second biopsy specimens was similar to that of the first biopsy, while the number of mesangial cells expressing α-SMA and the index of renal sclerosis were higher in the second biopsy than in the first biopsy. The indexes of renal sclerosis were higher in children with more macrophages expressing MRP8 than in children with less macrophages expressing MRP8. Our results suggest that renal macrophages expressing MRP8 may be involved in the progression of sclerotic changes in children with IgAN.