This study aims to analyse how Japanese first-year university students' writing anxiety in academic writing classes changed over nine months. A total of 102 Japanese first-year university students participated in an academic writing class. Two assessors evaluated the students' compositions, using the same writing assessment rubric. The students were divided into three groups--low, middle, and high proficiency groups--based on the results of a placement test before entering university. The students also completed open-ended questionnaires and the Second Language Writing Anxiety Inventory (SLWAI). Multivariate analysis of covariance was conducted to examine the difference in SLWAI scores for the first, middle, and final writing tests and among low, middle, and high proficiency groups. The results showed that the students in the high proficiency group had different writing anxiety tendencies. It was found that somatic anxiety in students in the higher-level English proficiency group decreased, and that cognitive anxiety was reduced for the students in all proficiency groups. On the other hand, avoidance behaviour anxiety was not decreased. The results from the questionnaire showed that writing anxiety might be related to English proficiency, because the ideas about academic writing varied among the different proficiency groups.