The purpose of this study was to investigate effects of extensive reading on acquisition of English collocation. 12 university students in Jeonbuk province participated in the extensive reading program for 9 weeks. The effects of extensive reading on acquisition of English collocation was determined based on the increase in a collocation test, a book report, a survey, and an interview. It was revealed that extensive reading influences acquisition of English collocation. First, the participants learned grammatical and lexical collocations. The outcomes of the collocation test showed that grammatical collocation was improved more than lexical collocation. Second, extensive reading had an effect on acquisition of the productive and receptive knowledge of both grammatical and lexical collocations. Receptive knowledge was developed more than productive knowledge based on the scores of the collocation test. Third, extensive reading worked better with the participants who had higher reading ability than those with low reading ability. The participants who read Stage 2 improved in the collocation tests more than those who read Stage 1. Forth, the participants used grammatical and lexical collocations in the book reports. The average number of the collocation use was 5.95 each book report and grammatical collocation was used more than lexical collocation. Last, the survey and the interview showed that the participants recognized that they have to learn collocation and extensive reading helped them to learn and acquire grammatical and lexical collocations. Based on the results, it is suggested that various extensive reading materials and activities are needed.