How should I say...it can look like the same...but a little different nuance . 아니에요 : just NO. politely. wider using. 아닌데요 : politely and same meaning.. it's basically..an interrogative sentence. like this...^^ Umm.....Oh! Did you make a reservation? Let me see...... hmm....No..-_-?(아닌데요?) Did you book it carefully?