We report a patient treated with rituximab for interstitial pneumonia (IP) associated with microscopic polyangiitis (MPA) and who was undergoing hemodialysis. A 59-year-old woman who had been treated with tacrolimus for 1 year for rheumatic arthritis was referred to the Department of Nephrology for fatigue, fever, weight loss, and rapidly developing renal dysfunction. On the first admission, severe renal dysfunction, proteinuria, hematuria, and an elevated titer of MPO-ANCA were observed, and the woman was diagnosed with rapidly progressive glomerulonephritis because of MPA. At that point, IP was found to be present but not active. Although steroid semipulse therapy following an initial prednisolone (PSL) administration of 40 mg/day, IVCY, and plasma exchange were administered, renal dysfunction did not recover, and the patient required maintenance hemodialysis. Upon discharge, a high titer of MPO-ANCA was continuously observed. Nine months after the initiation of hemodialysis, respiratory discomfort and desaturation developed. Interstitial shadow and ground glass opacity were seen on a CT scan, and the patient was diagnosed with exacerbation of interstitial pneumonia caused by MPA recurrence. At the second admission, acute findings identified by imaging techniques had improved. However, the high titer of MPO-ANCA continued in spite of the steroid semi-pulse therapy following PSL administration, and rituximab corresponding to 200 mg/weekly for 1 month was also administered. The dose of rituximab was decreased subsequently because the patient was judged to be compromised by the hemodialysis. At the same time, internal administration of sulfamethoxazole/trimethoprim was initiated. After the rituximab treatment, MPO-ANCA antibodies gradually decreased, and the respiratory condition improved. Five months after the rituximab treatment, respiratory dysfunction recurred. Based on the CT findings and a high level of β-D-glycan, the patient was diagnosed with ARDS due to pneumocystis pneumonia. In this case, rituximab was effective for IP due to MPA, but pneumocystis pneumonia could not be prevented in spite of prophylactic antibiotics. This case suggests that deliberative dose adjustments, careful patient observation, and prophylactic measures for infection are critical in rituximab treatment.