Writing is a course provided for the English Department students since it is one of important skills that must be mastered. However, the process of writing itself is not easy so errors easily appear. In order to decrease the number of errors in writing, types of the errors and the possible causes are sought. By knowing types of errors and the possible causes, it is hoped that teachers can apply some crucial things suggested in this study in order to make the students' understanding about passive voice construction more complex. This study reports what kinds of errors of passive voice construction found in the explanation composition of English Department students and the possible causes of the errors.