A 27-year-old Japanese female developed nephrotic syndrome and impaired renal function during pregnancy. A renal biopsy performed at 21 weeks of gestation revealed crescentic IgA nephropathy. She was treated with steroid pulse therapy followed by conventional steroid therapy. Although the nephrotic syndrome was persistent, the impaired renal function did not deteriorate after the treatment. A live infant was delivered by cesarean section at 37 weeks of gestation. After the delivery, both the nephrotic syndrome and renal insufficiency improved gradually. The indications for renal biopsy and treatments for active IgA nephropathy during pregnancy are discussed.