This study investigated the effects of Cooperative Learning on seventh graders’ vocabulary learning in China. This study was conducted because in China, students usually learn vocabulary via traditional learning method-rote memorization. However, this method has a lot of issues. For example, students only know how to write the words but they cannot use them in contexts. Students tend to forget new words they have newly learned. The purpose of this study was to find out whether Chinese secondary school students can benefit from Cooperative Learning in vocabulary; whether Cooperative Learning can help students in applying new words and whether students can retain new words longer using Cooperative Learning. This research followed a quasi-experimental design, with an experimental group and a control group. Data were collected in a secondary school in Beijing, China. The participants took three tests: a pretest, post-test and a delayed post-test. A one-way repeated ANOVA was used to analyze the data in SPSS (25.0). The findings showed that there was a significant difference across three time points in the two groups (p < .001). There was no significant difference in the students’ vocabulary scores between the two groups (p > .05). However, it was found that there was a significant interaction between time and group on students’ vocabulary learning. An ANCOVA analysis showed that there was a significant difference between the two groups in the delayed post-test (p = .01). These findings can be beneficial to the professionals who work as English teachers in secondary schools in China. My results suggest that Cooperative Learning may be helpful in improving students’ vocabulary learning outcomes.