Recent research efforts in teacher education have focused on innovative instructional delivery with little attention to learner-related variables such as language anxiety and prior- knowledge that can affect learning outcomes in English essay writing. Notwithstanding these interventions, the problems of mass failure and poor quality of essays still persist among EFL students majoring English language. Therefore, the current study examined the relationship between language anxiety and prior knowledge on EFL students' performance in essay writing. The research adopted a descriptive research design of survey type. Data were collected using two research instruments: Language Anxiety and Prior Knowledge Questionnaire and an Achievement Test in Expository Writing. Three hypotheses were tested at a 0.05 level of significance, and 350 students were randomly selected. The results showed that there were significant relationship between the independent variables and students' achievement in expository essay writing.