This study investigated EFL teachers' underlying assumptions about assessment and how these assumptions are congruent with current perspectives in assessment. Informed by interpretivist philosophical underpinnings, the study adopted qualitative research approach. Nine teachers from three universities located in western Ethiopia participated in the semi-structured interviews, and the data were analyzed using thematic and content analysis approaches. Generally, the findings revealed complexity and diversity in teachers' assumptions, which centered on four emergent themes: knowledge/content, valid approach to assessing knowledge, values and judgements, and power relations. Most of the teachers' assumptions are contradictory with current perspectives and the expectations of the recent reforms on classroom assessment. A few modernist assumptions that teachers held even could not always translate into practice, suggesting the influences of contextual and institutional factors that should be further studied. The need to help EFL teachers develop contemporary assumptions in foreign language assessment is the primary implication of the study. Findings of this study can be considered as one of the necessary steps towards developing a new measure of assumptions about assessment that can be used to assess the underlying assumptions embedded in EFL teachers views and practices of assessment.