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Algebraic mistakes are one of the obstacles to learning various mathematical topics and progressing in higher education. Knowing about the causes of these mistakes plays an important role in improving the education system. Therefore, the present study aims at examining the opinions of mathematics teachers about studentschr('39') educational mistakes in algebra. This research is qualitative research that its sample includes 8 middle school math teachers who were selected using the purposive sampling method. In order to collect data, Semi-structured interviews were used and data were analyzed using the coded method and the Categorize similar content. The findings of this study showed that the three categories of "knowledge acquisition process", "student individual characteristics" and "teaching elements" are usual and specific reasons for studentschr('39') mistakes in algebra from the teacherschr('39') viewpoint.