This research investigates whether a flipped classroom with Communicative Language Teaching (CLT) approach can lead students to increased gains in speaking skills within an undergraduate English class at the Royal University of Phnom Penh, Cambodia. This was designed to utilize pre-class online videos to replace live "chalk and talk" lectures, with a variety of CLT activities implemented during class time, including discussion-based learning, pair and group work, role play, and games. A mixed method was used to analyze different sources of data, including pre- and post-tests on speaking, written one of grammar and vocabulary, and observations. The experiment was employed with 21 freshmen of an academic year of 2017-2018 (n=21) to determine any differences in their speaking achievements that might be associated with a flipped classroom and CLT. The results from the observations and pre and post tests indicated that the participants not only enhanced their speaking ability but also changed their attitude toward learning English. These results specified that the flipped instruction with the CLT activities were effective in improving the participants' speaking ability which significantly contributed to better learning outcomes. Therefore, it is recommended that English language teachers in Cambodia consider implementing a flipped classroom and CLT approach in their classrooms.