Silica gel films were prepared on Si(100) substrates from Si(OC₂H₅)₄- and Si(OCH₃)₄-derived sols by dip-coating, and the gel films were heat-treated at 100–700°C. The durability of the films against water was evaluated by measuring the thickness before and after soaking them in 80°C water for 24 h. The durability increased with increasing heat-treatment temperature principally due to the progress of film densification. Higher amounts of water for hydrolyzing Si(OC₂H₅)₄ were greatly effective in achieving higher durability at lower heat-treatment temperatures. Longer sol aging was also effective in improving the durability of the Si(OC₂H₅)₄-derived films. Si(OCH₃)₄-derived films exhibited much higher durability than Si(OC₂H₅)₄-derived ones. All of these factors, i.e. the larger amounts of water for hydrolysis, the longer sol aging time and the employment of Si(OCH₃)₄, may provide more dense film structure and more chance to undergo condensation during gel film heat-treatment, leading to the higher durability at lower heat-treatment temperatures.