This study aims to find out students’ critical thinking skill, students’ skill in writing argumentative text, and effect of students’ critical thinking on improving skill in writing argumentative text in Interpretive Reading and Argumentative Writing course. Data were collected from seventy-five students batch 2015, selected from the second year of EED UMY undergraduate students. The researcher used the adapted questionnaire from Mincemoyer and Perkins (2005) to measure critical thinking level. Furthermore, the students’ score of argumentative writing data were taken from writing argumentative score. The data were analyzed using descriptive statistic and simple regression in SPSS 16. Simple regression was used to see the effect of critical thinking toward students’ argumentative writing skill. The findings showed that students’ critical thinking skill was in the high level (70-80) and students’ score in writing argumentative text was in the good level (61-85). The finding also showed that number of sig. was 0.869 > 0.05 meaning there was no significant effect of students’ critical thinking skill toward students’ skill in writing argumentative text. Critical thinking ability has no significant effect to students score in writing argumentative text.