The ability to write academic papers is required of university students for their undergraduate studies in hong kong and beyond. The key features of academic writing include (but are not limited to) the formal style and objective tone that distinguish such kind of writing from colloquial expressions or even many other types of writing that students do in secondary school. This chapter investigates a lexical approach to teaching formality, which has been informed by prior research (bei, 2013; heylighen & dewaele, 2002), in l2 academic writing classes of hong kong undergraduate students. Two classes of first-year students, randomly assigned to a control and an experimental group, participated in this three-week research. They received four sessions of intervention, one on conventional formality topics such as apa style and mechanics (the control) and the other on lexical formality, over a period of two weeks and subsequently wrote their midterm papers at the end of the third week. All essays were analysed with coh-metrix in terms of their structural complexity and lexical aspects. Teacher rating of the overall writing quality was also conducted. The results showed that the experimental group were able to use more noun phrases and fewer personal pronouns, indicating an awareness of the typical formal style of academic writing. This teaching approach also appeared to help student with a wider range of word choices, as shown in the higher type token ratio of the papers. However, the difference between the two groups in global writing scores rated by the teacher was barely significant. Neither the structural complexity nor lexical sophistication of their writing was in any way affected by formal vocabulary training. 2018 Nova science publishers, inc. All rights reserved.