Abstract: DNA in red paddy soil was amplified by polymerase chain reaction(PCR) through specific primers of 16S rDNA gene of anaerobic ammonia-oxidizer.PCR product was purified,cloned and sequenced.A 502 bp sequence of 16S rDNA gene of anaerobic ammonia-oxidizer belonging to Planctomycetes was obtained.Quantity of anaerobic ammonia-oxidizer in the red paddy soil during the rice growing season was monitored by the real-time PCR.The standard curve was made using the plasmid DNA with this rDNA sequence.The results showed that anaerobic ammonia-oxidizers existed in the surface as well as the root zone of the red paddy soil.The quantity changed during the rice growth season.The quantity of anaerobic ammonia-oxidizers in the surface soil increased gradually during the growing season.On the other hand,in the root zone,the number of the bacteria in the soil increased only at the late stage after booting.The anaerobic ammonia-oxidizers might contribute to the nitrification in the red paddy soil.