The purpose of this study was to investigate middle school mathematics teachers' knowledge for teaching algebra. The participants of the study were 48 mathematics teachers from various middle schools. A questionnaire was conducted in order to collect data about the teachers' knowledge related to teaching of algebra. The results showed that the participating teachers were competent in making transitions among different algebraic representations. However, they had difficulties in explaining the conceptual bases of some of the algebraic concepts and procedures. In addition, results indicated that some of the teachers had difficulties and misconceptions similar to those of students as depicted in the scenarios provided in the questionnaire.