The knowledge of NOx concentration in the exhaust gas of an oxy-fuel combustion system is very important for an appropriate design of the subsequent carbon capture process. NOx final emissions in oxy-fuel combustion depend on the reburn reactions of the recycled NO when it returns to the boiler. HCN is the main intermediate during this process, and thus, it may interact with NO significantly. The present work aims to evaluate the gas-phase interactions between HCN and NO in a CO2 atmosphere, characteristic of oxy-fuel conditions. A flow reactor experimental and kinetic modeling study of the oxidation of HCN in the presence of NO has been performed in a CO2 atmosphere and in the 973-1423 K temperature range. The influence of the stoichiometry and NO inlet concentration is analyzed. The results indicate that the HCN-NO interaction results in the diminution of both HCN and NO in a CO2 atmosphere. The conversion of NO is higher as temperature, oxygen concentration, and HCN/NO inlet ratio increase. The maximum NO reduction achievable is similar for all stoichiometries, although the total fixed nitrogen (TFN) is higher as oxygen availability diminishes. The temperature interval for NO conversion is shifted toward higher temperatures in the CO2 atmosphere compared to N-2. Compared to experiments without NO in the reactants stream, the presence of inlet NO inhibits the oxidation of HCN in the entire temperature range except for the highest temperatures, where NO promotes HCN conversion. Results have been simulated with a detailed kinetic mechanism that includes the conversion of HCN (Gimenez-Lopez, J.; et al. Combust. Flame 2010, 157, 267), and the main pathways for HCN conversion in a CO2 atmosphere and in the presence of NO are determined.