Dry grinding of the powder mixture composed of magnesium hydroxide and gibbsite using a planetary ball mill followed by its heating was conducted to prepare MgAl2O4 spinel. Both the starting materials are easily converted to amorphous phase by intensive grinding within 60 min. The monolithic MgAl2O4 spinel phase can be obtained from the mixtures ground over 15 min by calcination at 900 degreesC. The reactivity of the mixtures ground over 30 min is not improved. Prolonged finding promotes the aggregation of ground fine particles, but the aggregates deflocculate into fragments after calcination.