High school students in Vietnam have low speaking proficiency (Ashwill, 2020) because they do not have speaking environment beyond the classroom. The literature has shown that application of voice recording enables students to improve their speaking skills (Pop et al., 2011, Yanju et al., 2017). However, these studies have compared students' speaking skills before and after doing voice recording based on the first and the last recordings but have not compared between two groups: control group and experimental group. The book chapter presents findings about the effects of online voice recordings on students' speaking skills. Participants was 78 high-school students divided into two groups: the experimental group and the control group. Students in the experimental group was required to make their recordings in pair twice a week based on the given topic during 12 weeks whereas the control group did not do any extra speaking practice outside the classroom. Pre-test and post-test were conducted with two groups. The interview was used to explore students' experience during their online speaking practice. The results show that the experimental group have outperformed the control group after the treatment in terms of syntactical complexity and fluency. However, there is no statistically significant difference in lexical complexity, accuracy. The students in the experimental group stated that voice recordings provided them an opportunity to speak English beyond the classroom and enhanced their speaking confidence significantly because their vocabulary, pronunciation, responses to the questions improved considerably.