This experimental study aims to investigate the effects of using collaborative learning to enhance students' speaking achievement. The study using a pre-test and post-test design was conducted with 35 undergraduate students enrolled in a fundamental English course at Bangkok University to examine their speaking achievement on an English oral test before and after they had participated in provided instructional tasks based on collaborative learning. To explore the students' views on the use of the collaborative learning, all of the students were asked to complete a student diary after finishing each task, fill in a four scale-rating questionnaire and join a semi-structured interview at the end of the course. The data was analyzed by frequency, means, standard deviation, t-test, effect size (Hedge's g) and content analysis. The findings reveal the improvement of the students' speaking performance and positive feedback from the students on the use of collaborative learning activities. The study provides some pedagogical implications and suggestions for further investigations. (Contains 6 tables.)