Classroom interaction is a vital factor for teaching and learning second language. Numerous studies were conducted by researchers to shed a light on different aspects of this concept. Many different features of classroom interaction were dealt with researchers such as feedback, questioning, concept checking. Code-switching during the lesson is one of that features. It has been a widely debated topic for researchers. For this reason, the aim of this action research is to see the L1 amount and purposes in a preparatory class. Results indicated that 4/1 lesson time was spent with L1 and teacher used L1 for different purposes such as increasing motivation, increasing comprehension, humor, and building personal relationships.