Explanatory-confirmatory research design, one of the mixed methods research designs, was used in this study to investigate Curriculum Knowledge developments of prospective teachers regarding algebra. Cross-sectional study method, as a type of descriptive research and one of the non-experimental research designs, was used to collect quantitative data in the study. In the qualitative part of the study, case study was used. The participants of the study were composed of 176 prospective teachers studying in the elementary mathematics education department of a university in Turkey, who were first, second, third, and fourth year students with equal numbers. Interview, observation (observation notes, lesson video recordings, in-class observation form), knowledge test were used as the instruments for the purpose of examining prospective teachers' curriculum knowledge development. Kruskal-Wallis test, which is a non-parametric test, was used to compare the means of prospective teachers' Algebra Curriculum Knowledge Test (ACKT) scores since these scores are not normally distributed. According to the results of the study, it was observed that knowledge levels of the prospective teachers in terms of curriculum knowledge developed as directly proportional depending on the class level. In addition, it was also observed that the knowledge of prospective teachers in terms of curriculum knowledge was not at the desired level. Also, considering the general centrality of prospective teachers' answers on the partially true A and partially true B categories, it can be already concluded that prospective teachers' curriculum knowledge is inadequate.