An easily assembled chair armrest composed an armrest support, a connecting portion, and an armrest revealed. The connecting portion with a lock head is selectively disposed on the armrest or the armrest support while a locking hole is arranged at the armrest or the armrest support without the connecting portion. A locking slot communicates with the inner side of the locking hole. The armrest and the armrest support are in a first assembled state when the lock head is mounted into the locking slot through the lock hole. Then the lock head is horizontally rotated a staggered angle within the locking slot so that a lengthwise central axis of the armrest and a lengthwise central axis of the armrest support are coupled. Now the armrest and the armrest support are fastened into one part to be in a second assembled state.
Thereby both structural strength and tightness are improved.