Abstract: An armrests adjustment device for a chair is provided. The armrests adjustment device is to be assembled on a center column of a chair and installed with two armrests. The armrests adjustment device has a joint mechanism, two horizontal arms and two adjustment mechanisms. The joint mechanism forms a fixing hole configured to be disposed around the center column Each of the horizontal arms has a joint end and an adjustment end, the joint end is opposite to the adjustment end, and the joint end connects with the joint mechanism. One end of each of the adjustment mechanisms is mounted at the adjustment end of the horizontal arm, another end of each of the adjustment mechanisms is configured for being installed on one of the armrests.