There has been increasing interest in Synchronous Computer-Mediated Communication (SCMC) as a resource for English learning, which can increase the availability of academic help outside of the classroom and offer opportunities to communicate with English speakers around the world. This study investigated the effects of online tutoring on college students' speaking proficiency and their meaning negotiation processes. Participants were 25 second-year, non-native English-speaking college students at a university of science and technology in central Taiwan. Data collected included pre- and post-tests of oral proficiency, as well as records of communication between tutors and students. A paired sample t-test was conducted to measure the students' speaking progress, while Varonis and Gass’ (1985) interactional modification model was adopted to analyze their meaning negotiation processes. The findings revealed that both the high proficiency (HP) and low proficiency (LP) groups made significant progress in speaking fluency, vocabulary, and accuracy and structure in the meaning negotiation processes, while only the LP group showed significant progress in pronunciation and comprehension. The analysis also revealed significant differences in meaning negotiation processes between the HP and LP groups. It was found that students’ negotiated turns produced plentiful language output, suggesting that meaning negotiation provided a rich avenue for them to practice their oral skills through constant rephrasing and elaboration.