This study compared the effects of pre-task and post-task focus on form on learners in learning the English passive voice. 127 EFL students from a Chinese junior middle school were assigned to three groups: pre-task group, post-task group and control group. In the pre-task group, students’ attention was first drawn to the rules and usage of passive voice and then to communicative activities and tasks. In the post-task group, communicative tasks were conducted first and then rules and usage of passive voice were covered. The control group only finished tests without receiving any instruction. Students’ acquisition of passive voice was measured through pretest, immediate posttest and delayed posttest of an error correction test and a picture description task. The results show that both pre-task and post-task focus on form can help learners in learning passive voice, and on the whole, pre-task focus on form has better effect than post-task focus on form.