According to Genesis, God shut the door of Noah’s Ark after the survivors entered.
Genesis describes Noah, his family, and the animals entering the Ark before the flood. Once they are inside, the text says that the LORD shuts the door behind Noah. The detail emphasizes divine protection at the moment the flood begins and marks the boundary between safety inside the vessel and destruction outside it.
The answer is sometimes given as Noah because he is the Ark’s builder and organizer. However, Genesis assigns the closing of the door to God. This is a small but precise detail that many simplified children’s retellings omit or change.
The passage also presents the Ark’s occupants as entering in accordance with God’s command. The door’s closure therefore functions as the final act before the waters rise, rather than as an ordinary human task performed after boarding.