The purpose of this study was to describe the effect of multiple knowledge representations of physical and chemical changes on the development of primary pre-service teachers' cognitive structures. The study took place in an introductory general chemistry laboratory course in a four-year teacher education program. Multiple knowledge representations in chemistry refer to the macroscopic (visible), sub-microscopic (invisible), and symbolic (formulas and equations). The study adopted one group pretest-posttest design supported by qualitative data. Forty primary pre-service teachers participated in this study. The results revealed that enabling the primary pre-service teachers to learn multiple representations of physical and chemical changes was effective in developing both groups of pre-service teachers' cognitive structures, low and high-level understanding of particulate nature of matter, the latter benefitting the most. This finding was instructive because it emphasizes the difficulty that some primary pre-service teachers had on the particulate and symbolic representations of physical and chemical changes. The improvement in primary pre-service teachers' cognitive structures of physical and chemical change by the use of multiple representations.