The purpose of this study is to investigate the effect of sitcom, as an authentic video, on English speaking ability. The study was conducted among 55 in two 10th grade classes. English lessons have been held for 8 weeks in a high school. Each week both control and experimental groups were exposed to the same themes. However, while interactive speaking activities were done with the control group, experimental group watched an American sitcom called "Monk" and did video activities based on speaking. Results revealed that when the mean of the test scored are compared, the experimental group who had been exposed to authentic video scored higher than the control group. Furthermore, an increase could be observed when the pre-test and post-test scores of experimental group were compared. Similarly, there was a significant difference between the post-test scores of experimental and control groups. The interviews have showed that students as well as their teachers' have seen considerable improvement in their English speaking abilities. As a result, the use of sitcom as an authentic material in English language education can be a significant language tool to contribute to the speaking abilities of English language learners.