Dicyandiamide (DCD) is commonly used as nitrification inhibitors which has the potential to reduce nitrogen loss from paddy soils. In paddy systems, periphytic biofilms are commonly presented at the soil/water interface and show significant effects on nutrient cycling. However, the interaction between DCD and periphytic biofilms in paddy and subsequent effects on nitrogen cycling is unclear. In this work, microcosm experiments were carried out to study the interaction between the periphytic biofilms and DCD and the potential influence on nitrogen cycling from in paddy. Results showed that DCD affected the development of periphytic biofilms, while the presence of periphytic biofilms accelerated DCD degradation. Results also showed DCD application reduced nitrification potential mainly by inhibiting ammonia-oxidizing bacteria (AOB). Higher DCD dosage increased NH3 volatilization loss. However, presence of periphytic biofilm reduced the NH3 volatilization loss but increased denitrification. Our work contributes to a better understanding on the nitrogen cycling processes in paddy, and provides useful information for the improvement of nitrogen utilization efficiency and the control of non-point source pollution. (C) 2020 Elsevier B.V. All rights reserved.