One of the more rapidly advancing subfields of second language acquisition research is Digital-game based language learning (DGBLL) and many studies have found that Commercial off-the-shelf (COTS) games can have a positive effect on vocabulary acquisition. COTS games are specifically made for entertainment purposes, while serious games, which studies have found to enhance language and content knowledge, are designed for educational purposes. In the present study, a serious game titled Slave Trade was adopted to examine whether vocabulary and knowledge of history can be acquired at the same time and to investigate how the participants perceived the serious game regarding language and history learning. Sixty six college EFL students were recruited to take part in this study. They were required to take pre- and post-tests in both vocabulary and content knowledge and to respond to a user survey. The study found statistically significant improvements in both vocabulary and history knowledge. The vocabulary learning can mainly be attributed to the rich contextual clues of the gaming environment and repetitive exposure to the target words (i.e. more than six times). However, it was also found that words of fewer occurrences could be acquired because of the gaming environment. In addition, the students reported that they had enjoyed a positive learning experience via the serious game. Finally, it is suggested that language teachers should consider making educational use of serious games.