. Nitrogen is the main fertilizer to increase rice production. Nitrogen fertilizer use efficiency is affected by organic matter content in the soil. Understanding decomposition and nitrogen release of plant materials is important to better manage organic inputs. The objective of this research was to study the nitrogen dynamics on flooded soil with rice straw compost application. The experiment was carried out in green house of Indonesian Soil Research Institute (ISRI) on October 2010 to January 2011. Soil samples were taken from Ciruas, Banten. The analysis of ammonium and nitrate were conducted 14, 20, 30, 40, 50, and 60 days after planting. The result showed that ammonium and nitrate in soil with straw compost applications were lower than that of chemical fertilizer application. After day 20, the concentration of ammonium in soil decreased to the same level for all treatments. The concentration of nitrate, after increase on day 40 decreased until the last obeservation (day 60). Nitrogen concentration in straw was higher under chemical fertilizer than that of straw compost application. In rice grain, N concentrations were not significantly different among the two treatments.