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This study explored how Mathematical Inequality topics are covered in Indonesian secondary-school Mathematics textbooks. This choice is due to the fact that Inequality topics are widely considered as an important topic yet very difficult topic for students. Several books published by Ministry of Education of Indonesia were selected and then analysed by employing content analysis method, and using vertical and horizontal analysis. The result showed that the textbooks pay little attention to Mathematical Inequality topics, especially quadratic Inequality. Nevertheless, absolute value inequality topic is well covered since, for example, various representations were provided in worked examples. This study hopefully could influence curriculum designers and/or textbooks’ authors in order to review and update related curriculum and/or the Mathematics textbooks.