Introduction:  Vocabulary has been of primary importance in recent EFL finding, because it is an important factor in second language proficiency. After becoming proficient in pronunciation and grammar, a student needs more time to work on his vocabulary, so that he/she becomes proficient in vocabulary. In spite of great satisfaction with and the importance of this field, there are still some important questions about second language vocabulary acquisition which need to be answered. Since these questions are not answered yet, the field of vocabulary remains somehow limited. One of the most important unanswered questions is what the effect of narrow reading (a kind of narrow input) is on vocabulary development. In this thesis, we investigate the effect of this kind of reading input in two levels: topic- limited lexical development and author- limited lexical development. Seventy five intermediate students were divided into three groups of equal number of students. Two classes were selected randomly as the experimental group. We gave a pre- test on the first category of vocabulary. After a week, the treatment for the experimental group started. A week after the end of the treatment, a post test was given to all three classes. The results show that author- limited narrow reading was more helpful than topic-limited narrow reading and non- narrow reading. ANOVA and post hoc comparisons between the three groups showed a great difference among the groups. The comparisons showed that those who studied using author-limited narrow reading developed their knowledge of vocabulary more than the participants of the control group.

Keyword: What Is Vocabulary?, Frequent vs. Non-frequent Vocabulary, Core vs. Non-core Vocabulary, English Vocabulary Size, English Native Speaker’s Vocabulary Size, Non-native Speakers’ English Vocabulary Size, Where Is Vocabulary Stored?, What Is Word Knowledge?, Implicit VS. Explicit Vocabulary Learning, Language Learning Strategies, Definition of Learning Strategies, Importance of Learning Strategies, Classification of Learning Strategies, Vocabulary Learning Strategies, Decontextualized Strategies/Activities, Partially Contextualized Strategies, Fully Contextualized Strategies, Vocabulary & Reading, The Role of Reading Materials, Narrow-input VS. Wide-input Reading, Review of Related Empirical Finding, OPT Placement Test, The First and the Second 1000-Vocabulary Tests., Instructional Treatment, On-line Vocabulary Profiler Software