The purpose of this study is to provide some implications for curriculum and instruction of buoyancy in secondary school science. The paper-test items about buoyancy in liquids based on the research of Zeineddin & Abd-El-Khalick (2010) were administered to 159 university students. The results of 91% students who had learned physics at high school showed the difficulty of description/application of the theory of buoyancy at different contexts. Although they described the theory of buoyancy, some students can’t perform scientific reasoning well at the other context. These difficulties are caused by memorizing the formula or rules without the understanding of conception of buoyancy in liquids.