Background Nowadays, English is used as an international language by the majority of countries of the world. As an international language, English is very important and has many interrelationships with various aspects of life owned by a human being. In Indonesia, English considered as the first foreign language and taught formally from elementary school up to the university level. People realize that teaching English at this level becomes very important.As an English teacher, he or she demands to explore effective techniques, method, and approaches. Reading is the good thing in life because it is a factor of great importance in the individual development and the most important activity in school. It is needed at every level of the field of the study.There are particularly in cases when students have to read English materials for their own special subject with a limited vocabulary anyone will also have limited understanding in terms of listening, speaking, 2 reading, and writing. It is true that it might be impossible to learn a language without mastering vocabulary. Vocabulary is one of the problems confronted by English language learners. It with a limited vocabulary, the learners cannot communicative to others clearly. Sometimes it is difficult to group the idea transmitted to them. The acquisitions of a large number of vocabularies can help to students listen, speak, read, and write. Mastering vocabulary is the ability to get or to receive lots of words and to know how to use the vocabularies in the context. By mastering vocabulary, students will know the meaning of vocabulary in the context and also help to avoid making mistake in reading a text.Collins and Collins (2002, p.8) says reading is a mental process. Although the eyes are involved in sending information about print to the brain, the brain performs the real act of reading. Then, reading is a mental process which involves deriving meaning and sending information about print to the brain till being the real action of readingAccording to Zwiers (2004, p.3), reading habits more clearly describes the automatic and unconscious processes that are involved in constructing meaning from text. Then, reading habit refers to the automatic process as the readers read the textual material and deriving meaning unconsciously. Zwiers (2004, p.3), adds comprehension habits are the split-second thought that kick in constantly to help a proficient reader actively construct meaning. Then, by building reading habit will constantly help the readers construct meaning actively. On the other side, Patel and Jain (2008, p.114) state that reading habits not only help the student to get knowledge and wisdom from the culture of heritage but are also very helpful in passing for leisure period.Moreover, Samrotul Muawanah on her research in 2014 which entitled “The Relationship between Students’ Reading Habit and Their Reading Comprehension”, stated that reading habit is proven as one of the factors that influence students’ reading comprehension.Students’ bad reading habit attitudes show impairment on their reading comprehension. However, she did not explain whether students’ reading habit is also as a great significance factor in students’ vocabulary mastery.There is need a research to find out “The effectiveness Students’ Reading Habit to Improve Vocabulary Mastery.” in Private Junior High School.Research Questions1. How is students’ achievement in English vocabulary mastery before reading habit treatment?2. How is students’achievement in English vocabulary mastery after reading habit treatment?3. Is there any significant influence of the application of reading habit treatment on the students? achievement in English vocabulary mastery?Research Purpose Based on the research questions above, these objectives of the research is to know: 1. To find out the students’ achievement in English vocabulary mastery before applying reading habit 2. To seek out the students? achievement in English vocabulary mastery after applying reading habit3. To reveal any significant influence of the application of collaborative learning method on the students? achievement in English vocabulary mastery Significances of The ResearchThe study of the research is expected to provide an actual result. Theoretically, the research may become a reference to improve young learners? achievement in vocabulary mastery. Practically, this research is expected that the young learners? will enrich their vocabulary mastery.