In spite of numerous studies on the effect of AIAT on foreign language learning, few have examined its impact on university students’ academic writing proficiency over an extended period. This study, therefore, investigated the effect of Google Translate (GT) on the writing proficiency of English as a Foreign Language (EFL) university students. It examined fluency, lexical density, accuracy, and syntactic complexity across four versions of students’ writings: the pretest, writing with the aid of GT, the posttest, and a retention test conducted two to four months after the treatment. The findings indicated that syntactic complexity, accuracy, and fluency improved when students used GT for writing; however, these measures showed a significant decline in the posttest and retention test without GT. This decrease was more pronounced in lexical density and less so in syntactic complexity. Despite this decline, all factors assessed in the retention test still showed improvement compared to the pretest, indicating the positive effect of GT on students’ foreign language writing performance.
