Iron catalyst films for the growth of carbon nanotube (CNT) arrays are prepared using sol-gel technique during different hydrolytic periods. It is shown that the extent of hydrolysis of the catalyst precursor has strong impacts on the size and density of iron catalyst particles, which distributed on surface of the film. The iron catalysts formed big clusters in the early stage of the hydrolysis, whereas the particle size decreased dramatically to approximate 20 nm when the hydrolytic duration is as long as 150 h. The reaction between the hydrolytic product of ethyl orthosilicate and the iron oxide particles effectively influence the structure of catalysts during the process of annealing precursor films and reducing the iron oxide particles into iron catalysts. We believe that the hydrolytic product limits the mobility of the catalyst particles, preventing them from aggregating into big clusters by Ostwald ripening. This catalyst film may be utilized to create a template to control the length and quality of CNTs. (C) 2012 Elsevier Inc. All rights reserved.