English is a demanding language for EFL students especially ones without access to additional support like tutorials, extra classes, and opportunities to use English in their daily lives. Scaffolding the writing process for students and making automatic use of genre knowledge would help them improve their English writing performance. Little is known about how genre knowledge with scaffolding instruction can help undergraduate students write an argumentative text in English that is composed of complex stages and sub-stages, for them to write a good thesis. This study aims to explore if the use of scaffolded genre-based pedagogy applied in a writing process can improve the argumentative writing skills of undergraduate students. This study employs two-cycle action research involving 25 students enrolling in Argumentative Writing subject at the university. An observation form and documentation are used as the research instruments. Data from the observation and documentation were analyzed qualitatively. The results of the analysis have indicated that scaffolding students to write argumentative texts based on the genre of the text has assisted them in developing their writing skills.