This study is aimed at exploring the relationship between explicit instruction of mind mapping at pre-writing stage and the quality of Chinese EFL learners' argumentative writing. Thirty-nine first-year English majors from two convenient classes were randomly assigned into the experimental group and the control group respectively. For the control group, the traditional way of teaching writing was adopted, while for the experimental group, the application of mind mapping was integrated into the writing instruction. Five participants from the experimental group participated in the following interview. The comparison of mean scores of post-experimental argumentative writings between two groups indicated that the experimental group significantly performed better than the control group in content and organization of their writings. Through the analysis of interviews, it was found that participants regarded mind mapping as a useful tool for planning their writing and their personal attitudes toward English writing became more positive. The findings provide EFL teachers and curriculum designers with useful insights into improving the efficiency of writing instruction.