We report a case of APN after OSP use in a patient with nephrotic syndrome (NS). Renal biopsy revealed minimal change disease with multifocal calcium phosphate deposits within the tubules and in the interstitium. The serum level of fetuin-A, a systemic calcification inhibitor, was low during severely proteinuric state but normalized after remission of NS. To verify whether fetuin-A levels are low in NS patients, serum fetuin-A levels were determined in 10 patients with NS and 10 with asymptomatic microscopic hematuria (H). The mean serum fetuin-A levels were significantly lower in the NS group compared to the H group (p < 0.01). This finding suggests that a lower serum fetuin-A level may be associated with APN after OSP use in patients with NS, thus careful attention should be paid when colonoscopy using OSP is scheduled in this population.