Despite the burgeoning research interest in collaborative L2 writing, it is underrepresented in the literature regarding how teachers use such activities within real-world classroom settings. This case study seeks to offer a comprehensive understanding of the practices adopted by two EFL teachers in implementing collaborative writing within Chinese university contexts. Drawing upon Activity Theory, the study delineates the teachers' practices into two distinct activity systems, elucidating the production, distribution and exchange aspects of their activities taken in implementing a collaborative writing project. The findings reveal that while both teachers utilised a variety of instructional tools and pursued similar outcomes, they exhibited different features in the exchange and distribution aspects of their activity systems. The differences were manifested in their adherence to the norms, regulations and principles governing collaborative writing in their teaching environments, wherein the teacher, students and university each assumed distinct roles. Implications are provided for the effective integration of collaborative writing practices in language education.