This study aimed at examining the predictors of quality of science fair (SF) projects in the light of pre-service teachers' evaluation of SF rubric' domains. These projects were selected by judges in A city for the A Regional Exhibition of Science and Mathematics Project Study for Primary School Students: The SF projects were evaluated by thirty junior pre-service teachers who took the Projects Based Learning Applications course at A University A Faculty of Education in the Fall Term of the academic year of 2011-2012. The results of study revealed that the lowest mean scores of the domain of SF rubric was the method domain ([x-bar] = 1.35), and the highest mean scores of the domain of SF rubric was the utility domain ([x-bar] = 1.64) according to the results of the descriptive statistics. Surprisingly, the methods domain was one of the weakest predictors of overall scores of the SF rubric. It is important that project competitions and project based learning applications should do to help students to gain the scientific research skills. The necessary steps should be taken to help teachers and pre-service teachers to look at the science fair and preparing SF projects from this perspective.