DFT calculations are performed to investigate the catalytic activity of Ti-doped graphene nanoflake (Ti-GNF) in oxidation of ethylene to ethylene oxide by NO molecules. According to our results, this reaction proceeds in three steps. At first, two NO molecules are adsorbed on Ti-GNF in the dimer form and the reaction starts with the dissociation of (NO)2 into N2O and Oads species. Next, ethylene is oxidized to ethyleneoxy intermediate by Oads. Finally, the cyclization of ethyleneoxy results the ethylene oxide as a desirable product. The activation energies suggest that Ti-GNF is an efficient catalyst for the epoxidation of ethylene by NO.