Different diagnostic tools have been developed and used by researchers to identify students' conceptions. The present study aimed to provide an overview of the common diagnostic instruments in science to assess students' misconceptions. Also the study provides a brief comparison of these common diagnostic instruments with their strengths and weaknesses. A total of 273 articles published (from the year 1980 to 2014) in main journals were investigated thoroughly through document analysis method. The study reveals interviews (53%), open-ended tests (34%), multiple-choice tests (32%) and multiple tier tests (13%) as the most commonly used diagnostic tools. However, each tool has some advantages as well as disadvantages over the others that should be kept in mind in their usages. A careful user of a diagnostic instrument such as a classroom teacher or a researcher would be aware of the diagnostic instruments and selects the most effective one for his/her purposes.