Although there has been ample research on English as a Foreign Language (EFL) teachers’ formative assessment practice (FAP) and their agency separately, scant attention has been paid to the possible influence of teachers’ level of agency on their FAP. Accordingly, this study investigated EFL teachers’ FAP in the light of teachers’ agency. The initial participants, selected based on convenience sampling, comprised 180 male and female Iranian EFL teachers within the age range of 22 to 45. Their teaching experience fell between a few months to 21 years. The initial 180 teachers were given a Teacher Agency Questionnaire (TAQ) to determine teachers with high and low levels of agency. To this aim, 30 teachers who scored the highest and 30 who scored the lowest on the TAQ were selected. The 60 teachers were asked to fill out the Teacher Formative Assessment Practice Scale (TFAPS). Moreover, 15 teachers from each group were asked to take part in semi-structured interviews to explore their perceptions regarding their FAP. The results of parametric independent samples t-test revealed that teachers in the high-agency group scored significantly higher than their counterparts in the low-agency group in terms of both teacher-directed (p = .00<.001, effect size = 3.32) and student-directed FAP (p = .00<.001, effect size = 3.44). The descriptive and qualitative comparison of the thematic analysis between teachers in the high agency and low agency groups demonstrated marked differences both in the total number of themes and theme mentions as well as the theme contents between the two groups. Based on the findings, teacher educators are encouraged to enhance EFL teachers’ level of agency to improve their FAP.