Nobita’s grandmother recognizes him because she knows his face and, more importantly, immediately accepts him as her grandson even though he has grown up. In the story, she doesn’t treat him as a stranger; she simply senses who he is and welcomes him warmly.

How it happens

  • She sees the grown-up Nobita and still calls him her grandson.
  • The story frames this as an emotional, almost instinctive recognition rather than a mystery or trick.
  • Her reaction is also tied to the film’s theme: family love stays the same even when time changes people.

In the movie version

In Stand by Me Doraemon 2 , the grandmother accepts Nobita when he visits her in the past, and the scene is used to show her deep affection for him. She even tells him she wants to see his bride, which becomes a major emotional moment in the plot.

Simple answer

She recognizes current Nobita because she is portrayed as lovingly knowing that he is her grandson, even after he has grown older.

TL;DR: His grandmother recognizes him through their bond, not through a special clue or gadget.