Open source lectures not only provide knowledge-seekers with convenient ways to obtain knowledge and information, they also serve as potential language learning resources that provide extensive language input and repeated exposure to vocabulary within specific topics or disciplines. This current study aims to examine the relationship between English proficiency, lecture comprehension, and the acquisition of vocabulary through viewing OpenCourseWare (OCW) lectures on the Internet. Data was drawn from a pool of 65 college-level students learning English as a foreign language. Three open source lectures were selected from OCW lectures at MIT and Yale University. The participants' English proficiency and general comprehension of the three lectures were measured through pre- and post-testing to examine the effects of the lectures on vocabulary acquisition. The results of the study indicate that the learners with better English proficiency and better content comprehension acquired more vocabulary from viewing OCW lectures. Overall, learners were satisfied with the learning experience provided by the OCW lectures and considered the OCW lectures to be beneficial for learning English. (Contains 9 tables and 1 figure.)