Objective: This study investigated the clinical implications of serious infections in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV) who received the first cycle of rituximab (RTX) during the first 6 months of follow-up. Methods: The medical records of 36 AAV patients treated with RTX were reviewed. A weekly dose of 375 mg/m 2 RTX was administered for 4 weeks to all patients along with glucocorticoids. Serious infections were defined as those requiring hospitalization. All-cause mortality during the first 6 months of follow-up was counted. The follow-up duration was defined as the period from the first RTX infusion to 6 months after the first RTX infusion. Results: The median age was 60.5 years, and 16 patients were male. Seven of 36 patients (19.4%) died and three AAV patients had five cases of serious infection such as enterocolitis, pulmonary aspergillosis, atypical pneumonia, cytomegalovirus pneumonia, and cellulitis. AAV patients with serious infections during the first 6 months of follow-up exhibited a significantly lower cumulative survival rate than those without serious infections (p<0.001). However, we found no independent predictor of serious infections using the Cox hazard model analysis. Conclusion Serious infection is an important predictor of all-cause mortality in Korean patients with AAV who received their first cycle of RTX but there were no significant variables to predict the occurrence of serious infections at the first RTX. Thus, in cases refractory to other induction therapies, RTX should be strongly considered, despite an increase in mortality rate.