This study aims to analyze school principles' supervision practices according to teachers' opinions. The study employs phenomenology design out of qualitative research methods. The data of the study were gathered in 2019-2020 academic year from 16 teachers who had been working in state schools for 16 or more years through face to face interviews via a semi-structured interview form. The study attempted to reveal participating teachers' opinions on school principles' supervision based on their experiences with regard to teachers' professional development, motivation, affectivity and objectivity of supervision. The first finding of the study reveals that school principals' sharing experience, mutual work, being organized, overcoming insufficiencies and satisfaction contribute to teachers' professional development. Second finding of the study states that support, constructive criticism, appreciation and communication increase teachers' motivation. According to the third finding of the study school principals' administrator role, supervision knowledge, supervisor role and continuity are factors of effective supervision. Last finding of the study explains that impartiality, equity, sense of mission and meticulousness are needed for objectivity of supervision. Results are discussed and suggestions are provided.