An assembling structure of a ceiling fan has a motor shaft and a driving assembly mounted on the motor shaft. The motor shaft is mounted through the driving assembly. The driving assembly has an upper cover, a lower cover, a chamber, a circuit board, and a positioning mechanism. The lower cover has a covering board and a mounting cylinder mounted in a center of the covering board, and is mounted on the motor shaft via the mounting cylinder. The chamber is formed between the upper cover and the lower cover. The circuit board is mounted in the chamber. The upper cover, the lower cover, and the circuit board are sequentially arranged from top to bottom. The positioning mechanism is mounted in the chamber and limits a mounting position of the circuit board. The present invention solves the noise issue.