Abstract: Active magnesium oxide was prepared by the calcination of magnesite,and then used as binder for coal bri- quetting. The activity,specific surface area,crystal structure and morphology of as-prepared magnesium oxide were evaluated by N2 adsorption,scanning electron microscope (SEM) and X-ray diffraction (XRD). The bonding effect of magnesium oxide hydrates on coal and corresponding mechanism were studied by briquette compressive strength test, XRD and SEM. The results show that the activity of magnesium oxide increases and then decreases with the increase of the calcination temperature (from 500 to 900 ℃ ) and calcination time (from 0. 5 to 2. 5 h). The optimal calcination conditions are as follows:temperature of 700 ℃ ,time of 1. 5 h,therefore,the resultant magnesium oxide possesses a lower crystallinity,largest surface area and highest activity among all the samples prepared. The activity of magnesium oxide is the key factor to determine its bonding effect on coal particles. The magnesium oxide with higher activity may convert to more stable hydrate,and the corresponding briquette exhibit a higher compressive strength ( higher than 30 MPa).