Graded readers have been used as second language teaching material since the end of the Second World War. They are an important source of simplified material which provides comprehensible input on all levels. It is of crucial importance for a successful usage of graded readers in the classroom and in studies which focus on graded readers, that an adequate level of graded readers is chosen. In this paper the following will be explored: the theoretical background of choosing the adequate level of graded readers, explanation of the criteria for placement of graded readers in different levels, the differences in levels between the most important publishers and the selection of the adequate level of the graded readers. Furthermore, this paper presents preliminary research results, the goal of which was to test whether assigned CEFR levels represent a sufficient criterion for the selection of graded readers without previously testing reading skills or using tests provided by the graded reader publishers. Six subjects participated in the research; they were divided into three levels of English language knowledge (A2, B1, C1). Each participant read one and listened to another graded reader. In this research an interview was used for gathering data, the key component of which were text and audio material comprehension questions. The results showed that not all graded readers used in the study were adequate and that there are grounds for conducting further research with a larger sample.