A bicycle seatpost assembly comprises a first cylinder, a second cylinder, a positioning structure, an actuation structure, and a connecting rod. The second cylinder is configured to be telescopically received in the first cylinder. The positioning structure is configured to relatively position the first cylinder and the second cylinder. The actuation structure is configured to actuate the positioning structure and is disposed at a distal end of the first cylinder. The connecting rod is configured to operatively couple a control cable to the actuation structure. The connecting rod extends from the distal end of the first cylinder in a longitudinal direction of the first cylinder.