【Objective】 Iron redox processes under anaerobic conditions are closely correlated to nitrogen cycling in soils. Both nitrate-dependent ferrous oxidation (NDFO) and photosynthetic ferrous oxidation (PFO) are crucial pathways of biological ferrous iron oxidation. However, whether NDFO occurs in calcareous paddy soils and its relation to PFO is still ambiguous.【Method】 Soil samples were collected from Mengjin County, Henan Province, within the middle and lower reaches of the Yellow River. The soil samples were made into slurries using 10 mmol·L^-1 NO₃^-/NO₄⁺ solution or water at the very beginning. Then the slurries were anaerobically incubated under darkness or illuminated. On the 7th day of the incubation, we injected 0.5 mL 70 mmol·L^-1 NO₃^-or NO₄⁺ into a part of those slurries made with water to adjust their external NO₃^-or NO₄⁺ content to 10 mmol L^-1. To assess the iron reduction, and ferrous oxidation, Fe(II) in the slurries was measured dynamically using the phenanthroline colorimetric method. To evaluate the nitrogen transformation, NO₃^-and NO₂^-were analyzed dynamically using an ion chromatograph equipped with an electrical conductivity detector, and NO₄⁺ was measured after the incubation by 1 mol·L^-1 KCl extraction-Kjeldahl method. To fractionate the PFO, O₂ in the headspaces was determined dynamically using a portable fiber-optic trace oxygen meter.【Result】 The results showed that, though no apparent ferrous oxidation was observed, iron reduction rate decreased by 0.28 mg·g^-1·d^-1 and 0.33 mg·g^-1·d^-1. Also, the iron reduction rate constant was decreased by 0.15 d^-1, and 0.17 d^-1 in slurries under darkness with NO₃^-or NO₄⁺ amended at the very beginning. Ferrous iron was oxidized by 2.21 mg·g^-1 and 0.68 mg·g^-1 in slurries with NO₃^-or NO₄⁺ injected on the 7th day of the dark incubation and by 1.99 mg·g^-1 in slurries incubated under light. In addition, Fe(II) in the slurries was negatively correlated to O₂ in the headspace. Importantly, the reduction of NO₃^-to NO₄⁺ occurred in the slurries with NO₃^-injected on the 7th day of dark incubation.【Conclusion】 Ferrous oxidation caused by NDFO was observed in the calcareous paddy soil amended with 10 mmol·L^-1 NO₃^-and incubated anaerobically under darkness. However, the oxidation could be inhibited since the ferric iron resulting from NDFO would be reduced rapidly when the NO₃^-becomes depleted. Both NDFO and PFO occurred in the calcareous paddy soil incubated under illumination and the PFO resulted in 1.99 mg·g^-1 ferrous iron oxidized. Ferrous oxidation in soils under illumination was increased by 0.57 mg·g^-1 when NO₃^-was injected. These results help to further understand the redox processes and the coupled nitrogen transformation in wetland soils.