Although worm predation is effective for excess sludge reduction, it usually needs large land facility and high operational cost. In this study, Chironomid larvae (CL), a novel microfauna for sludge treatment was applied to a one-stage sludge reduction system (sequencing batch reactor, SBR). The results showed that adding CL induced the sludge reduction, and the sludge production rate was 31% lower than that in the control. Low volatile suspended solids/suspended solids (VSS/SS) ratio (0.77) and sludge volume index (70mL/g) were achieved. Moreover, adding CL did not deteriorate the contaminant removal (organic carbon and nitrogen), and the competition between CL and nitrifying bacteria for oxygen was beneficial for nitritation.