The aim of this study is to examine the cognitive errors as predictor of quality of life of mainstreamed elementary students. Quality of life is the degree of well-being felt by an individual. The functional deficiencies, which occur due to physical, cognitive, sensory, emotional disorders, affect the quality of life of the individuals. In this study, it is aimed to analyze the cognitive errors as the predictor of the quality of life of the mainstreamed students. The sample of the research was composed of 117 mainstreamed students (46 of the students are female and 71 of the students are male) selected by random sampling method who attend from first to fifth classes of a school under the control of Ministry of National Education in the academic year of 2007-2008 in Turkey, Samsun. The students were evaluated by the Children's Negative Cognitive Errors Questionnaire and Quality of Life Inventory for Children. The results of multiple regression analyses indicated that cognitive errors predict quality of life of the mainstreamed elementary students. The results of the Pearson product-moment correlation coefficient showed that cognitive errors were related to quality of life of the mainstreamed elementary students. Future studies are needed to replicate these results. Moreover, the relation between cognitive errors and quality of life were examined by self-report measures. In the future studies, different methods such as interview or observation could be used.