This study attempted to investigate the impact of extensive reading (ER) on the writing ability of Iranian EFL students. The study also took a further step to explore the effect of adding group work activity to the extensive reading program to find its possible positive effect on improving writing ability. The present study had two experimental groups with no control group. Participants were 35 students majoring in English Literature as ER plus GW (group work) group and 30 students majoring in English Language Teaching as ER group both taking the course of reading comprehension(II) in the University of Mazandaran. Participants were first given a reading comprehension test taken from TOEFL from which 24 students were chosen as the participants of this study according to their marks. The ER plus GW group read one graded reader each week at home, discussed the summary or related topic in the groups of five or six. The group members took notes on each other's talk including new vocabulary and language structure. At home, they wrote a summary of the book. ER group, on the other hand, read one book each week and wrote its summary at home without any discussion. Both groups were asked to write about a common topic one before and one at the end of the program as their pre/post test. Their summary examined in terms of four writing aspects including: run-on sentences, vocabulary errors (word choice and word form), and overall accuracy. The results of t-test revealed that adding group work to ER was almost effective in improving overall accuracy, run-on sentences, word choice but not in word form errors. Keywords: extensive reading, writing ability, group work, English literature, research.