The effect of organic carbon (OC) quality and quantity on switch between dissimilatory nitrate reduction to ammonium (DNRA) and denitrification (DEN) was studied in biofilter systems. High OC in matrix could promote significantly nitrate (NO3--N) removal due to the reinforce of DEN. Sodium acetate (SA) addition in influent further fueled NO3--N removal in groups with low OC in matrix but increased ammonium (NH4+-N) and nitrite (NO3--N) accumulation in groups with high OC in matrix. This indicated that high OC combined different species, facilitated the DNRA over DEN. Compared to bagasse, corncob was the better suitable OC source in matrix for DEN due to slow and continuous release of OC. Hence, in order to promote NO3--N removal and decline NH4+-N accumulation in biofilters, it is very important to screen suitable OC source (mixed utilization of multiple C sources is recommended) and regulate its dosage (below 80 mg L-1).