Writing is one of the four crucial skills that English learners try to master. Studies have shown that the writing motivation plays a significant role in English writing aptitude. This research tries to examine to what extent affective factors could foresee the academic writing ability of senior English majors to write English essays at School of Foreign Languages, Thai Nguyen University. To do so, a survey was conducted on a sample of 60 third-year students to investigate students' motivation and relevant factors that demotivate students in writing essays. The findings of the study are also affirmed by the use of semi-structured interviews delivered to around 15 respondents. The preliminary findings reveal that both linguistic and non-linguistic factors seriously influence the students. Lack of motivation amongst students is also attributed to student's insufficient background knowledge of some fields. Details of the study can be seen in the paper.