INTRODUCTION The diploma thesis entitled “The Use of Mother Tongue in EFL Classes” is aimed at promoting and enhancing the use of English language in EFL classes and at the same time allowing the mother tongue to be used in particular situations. The main focus of the thesis is on investigation of this phenomenon within the framework of frequency and diversity as far as secondary school students are concerned. There are many occasions in which students use the mother tongue excessively instead of English and the thesis attempts to identify these cases and suggest possible ways of solving them. There are several possible occasions for the usage of the mother tongue which might be beneficial and time-saving in the whole process of true understanding the grammar structures and rules of the foreign language. The use of the mother tongue should not be strictly prohibited in the situations such as complex instructions to basic levels, classroom management, negotiation of the syllabus and the lesson, language analysis, the presentation of rules (grammar, spelling, phonology and morphology), discussing cross-cultural issues, setting the scene, explanation of errors, checking comprehension, developing circumlocution strategies, checking for sense, methodology at basic levels and using translations to emphasize a recently taught language structure). (Auerbach 1993, Atkinson 1987, Schweers 1999). The thesis consists of two main parts. The first part is theoretical and includes review of previous research. The second part of the thesis is practical and is based on results of qualitative (action research) as well as quantitative research (questionnaires). MATERIALS AND METHODS The practical part of the thesis is composed of two phases. The first one focuses on finding out what the views of students about the Czech language being used within English lessons are, what amount of the mother tongue students use, what kind of opinions are held on under which circumstances and in which situations the mother tongue can be used. The second phase is intended to limit the excessive use of the mother tongue to only those situations mentioned above and to improve students speaking skills and promote self-esteem while using it. This phase concentrates on motivating of the students to use the English language more frequently by means of several activities including lessons primarily focused either on fluency or accuracy, choosing the topics which students are immensely interested in, inventing some materials for practice and better understanding of the grammar structures and the role play element. HYPOTHESES Several hypotheses have been determined to find out the excessive use of the students at their EFL classes. Here is a list of the set hypotheses: The students are afraid of making mistakes. The students are not motivated and interested in the topic. The students are not able to express their thoughts in English properly. EXPECTED RESULTS AND IMPLICATIONS The main goal of the research is to find out the reasons and factors leading to the excessive use of the mother tongue during EFL classes and the most effective ways of avoiding it. The additional aim is to create some materials with the students to be displayed in the class for them to be able to express some phrases in English. The study should highlight the problem of overusing the mother tongue in EFL classes not only by students but also by some English teachers. The thesis should also bring insights into possible ways of motivating students to express in English instead of the mother tongue. SOURCES 1)Atkinson, David. "The mother-tongue in the classroom: A neglected resource?" ELT Journal 44.1 (1987): 3-10. Print. 2)Auerbach, E. "Reexaming English Only in the ESL Classroom." TESOL Quarterly 27 (1993): 9-32. Print. 3)Schweers, W. Jr. "Using L1 in the L2 Classroom." English Teaching Forum 37.2 (1999): 6-9. Print.