A backrest adjustment structure for a boat seat includes a backrest and a bracket. A bottom of the bracket is rotatably connected to a seat of a boat. A back of the backrest is provided with at least two spaced pivot bases. An upper end of at least one of the pivot bases has an upper restricting portion. A pivot shaft is formed on a top of the bracket. The pivot shaft is rotatably pivoted between the pivot bases. The bracket is selectively engaged with the upper restricting portion. The leaning angle is adjustable, meeting the needs of players.