Backgrounds: Generally, treatment of asymptomatic bacteriuria is observation without medication. And this case showed continuous proteinuria and pyuria even after ACEi therapy for CKD and IgA nephropathy and circumcision. Case: Proteinuria was detected to 12-year-old boy in school urinary screening. Urinalysis showed proteinuria (3+) and pyuria (WBC 50-99/HPF). BUN (30.3 mg/dl) and creatinine (1.92 mg/dl) were increased. Calculated GRF is 41 ml/min/1.73m2. Escherichia coli was cultivated in urine culture. Kidney ultrasonography revealed increased cortical echogenicity of both kidneys and multiple small cysts in right kidney. Even though management with ACEi in 15 months and circumcision, proteinuria and pyuria has continued while no symptom of urinary tract infection was observed. Renal biopsy was done, which showed moderately advanced IgA nephropathy; widely severe tubular atrophy, interstitial fibrosis and no infiltration of inflammatory cells in interstitium. He was treated with pulse methylprednisolone for three consecutive days weekly for 3 weeks, followed by oral prednisolone every other day plus daily ACEi and probiotics contained Lactobacillus rhamnosus. Recent follow-up urinalysis showed decreased proteinuria (1+) and persistent pyuria. Conclusions: We report 12-year-old boy with CKD who continuously showed asymptomatic bacteriuria and was diagnosed as IgA nephropathy, used with methylprednisolone pulse therapy, oral prednisolone every other day plus daily ACEi and probiotics therapy.