Argumentative writing is one of the main writing types in Second Language Writing (SLW) instruction, as it links with the assessment of language capacity in tests. It is a common course for students of tertiary education, but few instructors have a clear comprehension of it. With the goal of giving circumspect teaching implications, this study serves as an illustration for argumentative writing lecturers in higher education. In this study, semi-structured interview, classroom observation and collected written drafts are used as research tools to discover the conceptualization and teaching practice of two lecturers who are instructing English-major sophomores. The findings show that different teaching beliefs (human-oriented and task-oriented) lead to different teaching process in argumentative writing class. Besides, the assessment criteria and students' response are revealed to understand the effects of those instructions accordingly.