Writing essays for EFL students is uneasy since they should have extensive knowledge on the topic, a good language use in vocabulary, grammar, and punctuation, and good motivation in writing. There are some factors that underlie these problems. This study aimed to find out students' perceptions on the affecting factors in writing descriptive essay. This research used a qualitative approach involving 41 students of Advanced Writing class. It utilized questionnaire and interview guideline. The findings showed that every student had distinctive factors that affected them in writing. Internal factors were those that come from inner student such as low motivation, limited vocabulary, lack of knowledge on organizing ideas, and low interest on the topics. Meanwhile, external factors were those that came from outside the individual such as learning atmosphere, learning facilities including dictionaries, hand phones, and laptops, and the role of their classmates and lecturers in writing descriptive essays. Based on the findings, it is suggested to the students to overcome the problems by brainstorming or outlining to help them organize idea. It is also suggested to them to maintain good motivation and interest in writing. Finally, it is recommended to conduct further study to solve EFL students' problems in writing and reduce the factors that hinder them in developing their writing skills.