The relationship between an individual’s actual knowledge and their self assessed knowledge about an issue is an important factor on consumer’s behaviour. The effect of the knowledge factor on consumer decision making is evaluated by two approaches which are objective (real knowledge) and subjective (self assessed) knowledge. In certain studies it was found that in some situations consumers believe they know more than they actually do about a topic; and they may make their decisions based upon the knowledge they assume is correct, whether it is true or not. This study aimed at determining the relationship between the objective and subjective knowledge about GM foods of consumers who live in the Hatay city centre. According to the research results; even though around 70% of the consumers thought that their knowledge about GM foods were ‘’enough, or relatively enough’’, correct response ratios of the four questions that were based on specific knowledge were quite low. In other words, consumers were overconfident about their knowledge of GM foods. Also, there was no correlation found between consumer’s purchase intention and knowledge level.