"Mathematical knowledge for teaching" is a concept indicating the requirement for a specific kind of knowledge required to teach mathematics. Mathematical knowledge for teaching necessitates a more complex structure than what is required to carry out mathematical tasks and the knowledge to do that. The purpose of this study is to realize the adaptation of "Mathematical Knowledge for Teaching--Geometry (MKT-G)" Test that was initially conceived in English to Turkish (or to Turkish culture). During the adaptation process; after the translations of the items, focus group interviews were held with a group consisting of mathematics teacher educators and experienced mathematics teachers, and then the data from 243 elementary mathematics teachers was analyzed via Item Response Theory (IRT). As a result of the analysis of the test items, psychometric values of the test items indicated that the items in the test performed well in Turkey. Besides, validity and reliability arguments were also tested. As a result, the Turkish version of the MKT-G test is highly reliable and valid to measure the teachers' knowledge of teaching geometry.