The research aims to describe the types of deviation of language politeness principle and the cause of deviation. The research was qualitative. The data of the research were all of the students’ speeches or oral conversation discourse and speech information situation. The data source was obtained from the students of class XI at SMAN 2 Panca Rijang Sidenreng Rappang.The data of the research were collected by recording, note-king, and unstructured interview technique. The data of the research were analyzed through four stages, namely data collections, data reduction, presentation, as well as data analysis and conclusions/verification. The results of the research reveal that the deviations of language politeness principle which were occurred in learning-teaching interaction in Bahasa Indonesia of class XI students at SMAN 2 Panca Rijang Sidenreng Rappang are single and double deviation. The causes of the deviation of language politeness principle in learning-teaching interactions in Bahasa Indonesia of class XI students at SMAN 2 Panca Rijang Sidenreng Rappang cover (1) deviation caused by the speakers intentionally accused the speaking partner, (2) intentionally speak not accordance with the context, (3) protective on opinion, (4) the speaker’s emotional impulse, (5) direct critic with harsh words, (6) mocking, and (7) no sympathy given to the speaking partner.              Penelitian ini bertujuan untuk mendeskripsikan jenis-jenis penyimpangan prinsip kesantunan berbahasa dan penyebab penyimpangan. Jenis penelitian ini tergolong penelitian kualitatif. Data dalam penelitian ini adalah seluruh tuturan siswa atau wacana percakapan lisan dan informasi situasi tutur. Adapun sumber data diperoleh dari siswa kelas XI SMA Negeri 2 Panca Rijang Sidenreng Rappang. Teknik pengumpulan data yang digunakan adalah teknik rekam, teknik catat, dan wawancara tidak terstruktur. Analisis data melalui empat tahapan,yakni pengumpulan data, reduksi data, penyajian sekaligus penganalisisan data dan penyimpulan /verifikasi. Hasil penelitian  menunjukkan  bahwa  penyimpangan  prinsip kesantunan berbahasa yang terjadi dalam interaksi belajar-mengajar bahasa Indonesia siswa kelas XI SMA Negeri 2 Panca Rijang Sidenreng Rappang, yakni penyimpangan tunggal dan penyimpangan ganda. Penyebab penyimpangan prinsip kesantunan berbahasa dalam interaksi belajar-mengajar bahasa Indonesia siswa kelas XI SMA Negeri 2 Panca Rijang Sidenreng Rappang meliputi (1) penyimpangan disebabkan oleh penutur sengaja menuduh mitra tutur, (2) sengaja berbicara tidak sesuai dengan konteks, (3) protektif terhadap pendapat, (4) dorongan rasa emosi penutur, (5) kritik secara langsung dengan kata-kata kasar, dan (6) mengejek, serta (7) tidak memberikan rasa simpati kepada mitra tutur.