The hydrophobic treatment of AIN powders. is commonly, used for depressing their hydrolysis process. A commercially claimed water-resistant AIN powder (hydrophobic treated) was investigated through hydrolysis with pH measurements of the suspensions. For comparison, an untreated AIN powder was studied with similar hydrolysis condition. The water-contacted powders were subsequently analyzed with XRD. Both pH measurements and XRD results indicated that the water-resistant AIN powders were not resistant to hydrolysis without surfactant addition. It was also found that the surfactant was effective in depressing hydrolysis of the hydrophobic treated AIN powders, but slowed down slightly the hydrolysis process for untreated AIN powders. A critical surfactant concentration of 0.7 wt.% was required for successfully depressing the hydrolysis process. (C) 2002 Elsevier Science Ltd. All rights reserved.