In this study, the modified Pechini method has been used to prepare alumina-zirconia mixed oxides with 0.5, 1, 25,40, and 75 mol% of alumina in zirconia. At low Al contents (< 25%), tetragonal phase zirconia was observed, while at higher At contents, the mixed oxide exhibited only amorphous phase. When they were employed as supports for Co catalyst for CO hydrogenation, it was found that the catalytic activities of low Al-modified zirconia supported Co catalysts increased by ca. 30% compared to the ones supported on pure zirconia or pure alumina, suggesting that the modification of zirconia by alumina has resulted in higher Co dispersion. However, when supports with high alumina contents (40-75 mol% At) were used, low Co dispersion and poor catalytic performance were obtained despite their higher surface areas. It is likely that cobalt formed metal support compounds with the amorphous phases of these mixed oxides. (c) 2006 Elsevier B.V. All rights reserved.