This study was conducted to examine how a collaborative social annotation tool can be used to support collaborative learning in translation instruction for EFL students. Participants were 100 undergraduate students who were English majors in a southeast university in China. An experiment with crossover design was carried out to examine the participants' learning and motivation in the social annotation-supported condition and the traditional instruction condition. The results showed that students received higher scores on their translation work and rated their perceived learning higher when they completed the translation assignments in the social annotation-support condition than in the traditional instruction condition. In addition, participants reported that they were more motivated when they completed the translation assignments in the social annotation-supported condition, though participants with different levels of language proficiency might be motivated by different reasons.