Speaking course at higher education has worthy responsibility and becomes pivotal foundation for the development of personal communication, intellectual, emotional, cultural, and social. This research aimed at developing Beach Ball Group Investigation (BBGI) cooperative learning model to improve social skill and investigating the effectiveness of this model in speaking course. The research design was Research and Development (R & D). The data were collected through questionnaire, interview, assessment sheet of social skill observation, and multiple choices. The data analysis employed t-test and n-gain to test the product effectiveness. The research result concluded that BBGI cooperative learning model was effective in improving student's social skill. It was indicated by coefficient value of tcalculation which was greater than that of ttable, as well as the difference between pre-test and post-test (n-gain) which was in good category.