Integrated rice-duck farming system (IRFS), as an environmentally friendly technology, has been applied and practiced in many provinces in China and some countries in Asia. There are various ecological effects to be proved in IRFS. This paper reviewed studies on the ecological effects of ducks on rice canopy structure, rice growth, yield formation, control of weeds, pests and diseases, natural enemies populations, paddy soil and water, rice quality and paddy environmental quality. The review indicates that further studies on ecological process and mechanisms in IRFS should be done.