The purpose of this research is to assess the effect of Voki, a tool of web 2.0 on students' academic achievement and attitudes towards English courses. The study group of this research, using a quasi-experimental design with a pretest-posttest control group, consists of 5th-grade students at a public secondary school in the Merkezefendi district of Denizli province, Turkey. In the experiment group, the "Party Time" unit was taught via Voki-supported activities while the same unit was taught according to the current curriculum without using Voki in the control group. The entire process of the experiment lasted 6 weeks. In the study, the academic achievement test and attitude scale towards English courses (Cronbach's Alpha = 0.92) were used to measure dependent variables. The normality distributions of the data were examined after the data were collected, and it was decided to analyze the data through the mean, standard deviation, and independent-sample t-test. According to the results of the research, there was an increase in the achievement test scores of both groups in the English lesson. However, a statistically significant difference was observed in the speaking section of the experimental group in the achievement test. There was no significant difference between the attitudes of the groups towards English courses. It is therefore recommended that English teachers should use Voki application in speaking activities.