The purpose of this paper is to investigate a novice primary teacher's mathematical knowledge in teaching on area measurement. Data were collected from a novice primary teacher of fourteen students in a primary school located in Ankara, Turkey using field notes, video recordings of lessons, and audio recordings of interviews before and after her teaching. Her mathematical knowledge in teaching was analyzed by means of the Knowledge Quartet model. The novice primary teacher's mathematical knowledge in teaching on area measurement was adequate regarding some of the codes such as choice of representations, making connections between concepts, and responding to unavailability of resources. However, her knowledge was inadequate in the codes of adherence to textbook, choice of examples, and responding to students' ideas. Implications and suggestions to improve teachers' mathematical knowledge in teaching are presented accordingly.