Credibility influences a user’s interest in a web site. Once users perceive the credibility of a web site they will be more likely to use it. A combination of factors affects such credibility – such as the provider, content, aesthetics, accessibility and solution of technical problems. The aesthetics of a web site can affect a user’s first impressions of credibility. Experiments have shown that users can judge a web site’s credibility in as little as 3.42 seconds merely on the basis of its aesthetic appeal. But what are the aesthetic factors that influence immediate judgment on web credibility? A study was conducted to ascertain these factors; first a framework of factors was suggested to develop a method focusing on the users’ actual perceptions in judging credibility based on aesthetics. This was done with 30 subjects viewing 13 pairs of images of recruitment agency web sites. ’Unity’ in design with its elements of balance, harmony, contrast and dominance was found to be an effective aesthetic factor resulting in immediate judgments on web credibility. These factors were presented for beginner web designers in online tutorials. This work is a result of MSc project.