Soil samples collected in paddy fields in Tianjin (TJ),Sichuan (SC),Jiangxi (JX) and Hunan (HN) provinces of China.The experiment was designed to have four levels of illumination,i.e.entire dark (D),light (L) and change from dark to light (D/L) and from light to dark (L/D) during anaerobic incubation of slurries prepared out of the paddy soil samples.Concentrations of Fe (Ⅱ) and chlorophylla (Chl a) were determined in the samples under incubation,to study effect of illumination on reduction of dissimilatory iron oxide.Results show that oxygen production of photosynthetic bacteria leads to oxidation of Fe (Ⅱ) in paddy slurry under anaerobic incubation.Light does not affect iron-reducing bacteria.Photosynthetic bacteria reproduce massively only in some paddy soils,and Chl a content increases first with illumination going on,and then levels off Anabaena sp.and Nostoc sp.of Cyanobacteria were identified respectively in TJ and SC soils,and both of these Cyanobacteria had the same Chl a absorption peak at 664nm,which suggests that oxygen production by photosynthesis Ⅱ occurred.A significant negative correlation was observed between Fe (Ⅱ) and Chl a content in the two calcareous paddy soils under anaerobic incubation.