The aim of this study is to investigate the effect of teaching integers by lesson study model on students' success and attitudes in mathematics. The research uses quantitative technique, "quasi-experimental design" with pre-test post-test control groups. The participants of the study are 62 sixth grade students and 4 teachers in three different branches at a middle secondary school in a district of Eastern Anatolia Region during the 2018-2019 academic year. There are two experimental groups and one control group in the study. In the experimentation phase of the research, treated groups were taught in accordance with the Lesson Study Model where teaching plan is generated in cooperation with teachers while the control group was taught in line with the MEB program. The study employs "Integer Achievement Test" (IAT) developed by the researcher as a data collection tool to measure the academic success of students in integers, and "Mathematics Attitude Scale" (MAS) developed by Baykul (1990) to measure their attitudes towards mathematics class. In the research, IAT and MAS are applied both as pre and post-tests for evaluation. The data obtained from the tests are analyzed with SPSS-22.0 statistical program. Because of the normal distribution of the groups in data analysis, one of the parametric tests, independent sample t-test is utilized. The findings reveal that pre-experiment scores of treated, and control groups were equivalent to each other in terms of mathematics academic achievement and attitude towards mathematics. After the application of the experiment, a significant difference in favor of the treated group is observed in terms of mathematics academic achievement. No significant difference between the scores of treated and control groups is found regarding average attitudes towards mathematics. Based on the findings of the research, it can be said that teaching carried out in line with the lesson study teacher professional development model increases student success but does not affect attitude towards mathematics class. Hence, it can be concluded that teaching with Lesson Study Model in mathematics class will have a positive impact on student success.