Abstract: In batch test, the denitrification performance of polycaprolactone(PCL)/starch blends and gravel supported system was investigated using PCL/starch blends as solid carbon source, and the component of the dissolved organic carbon (DOC) in water was also analyzed. The experimental results showed that PCL/starch blends could serve as the solid carbon source for denitrification of low C/N ratio wastewater without a nitrite accumulation. When ρ(NO₃^--N) was higher than 2mg/L, the denitrification reaction order of the experimental group (i.e., PCL/starch blends and gravel) and the control group (i.e., PCL/starch blends) were zero order reaction. The average denitrification rate for the experimental group was 7.214mg/(L·h), which was higher than 7.152mg/(L·h) of the control group. This indicated that most of the nitrate was reduced in the biofilm attached on the surface of PCL/starch blends. In addition, biofilm attached on the surface of the gravel was also used the DOC in the water for denitrification. At the end of denitrification reaction, microorganisms on the surface of the gravel were also involved in the degradation of carbon source of PCL/starch blends, resulting ρ(DOC) of experimental group was 74.50mg/L higher than the control group of 40.75mg/L. The pH of experimental and control groups decreased after increased first due to the comprehensive function of acidic substances and alkalinity produced in the process of degradation of solid carbon source and denitrification, respectively. The reducing sugar, protein and SMP-like substances were found in the DOCs of both experimental and control groups.