The purpose with this study is to examinate how preschool children reasoning about different objects possibilities to float or sink in different liquids. The liquids we used was water, milk and oil. Four children in the age 4–6 years old participated in this study. The method that has been chosen is interviews and observations. It is qualitative study that has been done. The study was initiated with interviewing the children about their assumptions about what will happen to the different things chosen for the activity.The activity was implemented under different occasions and with different fluids to make it easier to study their observations around each fluid. The children themselves have chosen an object they thought who would either float or sink. Together they chose an A-4 paper. The study also included three items that I had with me. The result of this study is that children already have knowledge of the phenomenon of floating and sinking. This was shown by the hypotheses they had to make before the materials were immersed in the liquids. However, they do not have knowledge of density as a concept. But they have a preconception that something affects the materials that make them either float or sink. The children used the language to understand and support each other in learning.     Keywords: Density, different liquids, float, physics in preschool, sink.