A combination of X-ray diffraction and thermal analysis was employed to characterise alumina hydrolysates synthesised from the hydrolysis of anhydrous trisecbutoxyaluminium (III). X-ray diffraction showed that the alumino-oxy(hydroxy) hydrolysates were boehmite. For boehmite the lamellar spacings are in the b direction and multiple d(0 2 0) peaks are observed for the unaged hydrolysate. After 4 h of ageing, a single d(0 2 0) peak is observed at 6.53 Angstrom. Thermal analysis showed five endotherms at 70, 140, 238, 351 and 445 degreesC. These endotherms are attributed to the dehydration and dehydroxylation of the hydrolysate. Alumina oxy(hydroxy) gels were formed from the hydrolysates of anhydrous aliphatic acid modified trisecbutoxyaluminium(III). X-ray diffraction shows the gels were expanded above the (0 2 0)-spacing of boehmite due to the incorporation of acid in the interlamellar space. The thermal analysis patterns of the acid modified gels were significantly different from that of the unmodified get.