This research is a qualitative study that examines the practices of teachers of science, mathematics, Turkish and social studies regarding interdisciplinary teaching approach. Participants in the study consisted of 35 teachers working in three different secondary schools with different socioeconomic backgrounds in the province of Adana in the academic year of 2016-2017. The data were collected by interviewing the participants through the "Demographic Characteristics Form" and "Interdisciplinary Teaching Practice Evaluation Form" developed by the researcher and analyzed by content analysis method. The results showed that the secondary school teachers performed the interdisciplinary teaching practices and that they influenced by the course goals and contents, information about different courses, characteristics of different students and extra goals. Interdisciplinary teaching practices are important in terms of promoting effective learning, having mental and emotional goals, and providing quality education services. It was revealed that both science and social sciences can be related to each other and to art lessons in the teaching process and the students are positively affected by the interdisciplinary teaching process. It was also found that teachers need guidance, adequate knowledge and skills, cooperation, and instructional designs or plans to guide them for practice.