There is scant research on preservice English as an additional language or dialect (EAL/D) teachers' paired practicums in an online context. Underpinned by Cultural Historical Activity Theory, this paper explores how preservice EAL/D teachers exercise their relational agency during online paired practicums. Data were collected from five preservice EAL/D teachers' weekly journals written during their paired practicums and interviews after they completed their paired practicums. Following the key components of relational agency, the thematic analysis highlights the dialectical relationship between preservice teachers' relational agency and different types of collaboration, evidenced by the formation of mutual objects, tool mediation, and shared expertise. This paper provides new insight into how preservice teachers' knowledge, especially related to the affordances of technology, may be expanded and mediated by collaboration.