A Study on Students’ Writing Ability in Rhetorical Structure of An Argumentative Essay of the Third Semester Students of ST-KIP ABDI Pendidikan Payakumbuh.

This research was descriptive quantitativeresearch, which used to know the students’ ability of writing rhetorical structure in introductory paragraph of argumentative essay, then the students’ ability of writing rhetorical structure in body (argument) of paragraph an argumentative essay, finally it was found that the students’ ability of writing rhetorical structure in concluding paragraph. In this research, the writer took the third grade students’ of English Department at STKIP ABDI Pendidikan Payakumbuh in 2012/2013 Academic Year. The number of English Department students were 30 students. In taking the samples the writer used the cluster random sampling because the writer chose the samples randomly.The instrument of this research was writing test. To know the validity of instrument the writer used the content validity because the second grade students of English Department had learnt how to make an essay. To know the reliability of this instrument, the writer used two scorers method: both scorers in this research were English teacher. Then, the data had analyzed by using Sudijono formula. Based on the result of the research at the second grade students’ ability of writing rhetorical structure in introductory paragraph of argumentative essay was fair (59.83), then the students’ ability of writing rhetorical structure in body (argument) of paragraph an argumentative essay was fair (54.12 ), finally it was found that the students’ ability of writing rhetorical structure in concluding paragraph was good (63.19).