Securing high electrochemical activity of nanomaterials is one of the most challenging issues in fuel cell electrocatalysts. Especially, in oxygen reduction reaction (ORR), inspiring breakthroughs have been made in activity enhancement based on fundamental knowledge about functional link between material structure and activity; for instance, Pt-M (transition metal) alloy electrocatalysts have surpassed commercial Pt/C by more than 30 times in mass activity. However, for more advanced electrocatalyst, a new functionality should be introduced on surface of nanomaterials which can open a new possibility of boosting electrochemical performance. Considering urgency for highly active and stable electrocatalyst, it is necessary to develop a new strategy to adopt various functionalities onto nanocrystals by post-treatment, and verify the origin of the boosted electrochemical properties. Here, we report introducing a new functionality on surface of Pt alloy nanocrystals with nitrogen dopants and their highly improved electrochemical activity as ORR electrocatalysts. Rational correlation between modified surface structure and electrochemical properties are discussed with various physicochemical and electrochemical analyses.