The purpose of this study is to figure out how WOM and critical reviews impact weekly box office revenues, and how the impact is different on mainstream and non-mainstream movies. The data of this study is from the motion picture industry of South Korea. 118 movies data was collected and movies were categorized into two groups by their distributors. The results show that the volume of WOM was positively significant to box office revenue, while the valence of WOM had no significant effect. The number and attitude of critical reviews had no consistent significances to weekly box office revenue, but the number of critical reviews was statically significant to the aggregate box office revenue. The effects of WOM were not statistically different between mainstream and non-mainstream movies. The effects of critical reviews, however, were different between mainstream and non-mainstream movies.