The latest curriculum for Swedish preschools (Lfpö98, 2010) stipulates that children should get more stimulation and guidance from teachers in order to increase their competencies and acquire new knowledge through their own activity. Mathematics is one of six domains which have been strengthened in the new curriculum and therefore it is important to investigate more about how children are using and how they are learning mathematics in preschools. The purpose of the present study is to explore and describe preschool children’s use of mathematics in their communication with others. This study is limited to examining situations in which children communicate with other children and adults. Moreover, the aim is to deepen the understanding of how preschool children use mathematics to convey mathematical meanings with other children and adults in preschool. The research questions was: How do children communicate mathematics? In what kind of situations does mathematics occur in their communication? What mathematical content is communicated? The theoretical framework was selected from a sociocultural perspective, which is a collective term for theories which assume that language's original function is communicative and that it is a means of social interaction. From a socio-cultural perspective, language, culture and children's actions are seen as essential elements of childhood development and learning. Prerequisites for this development include children’s participation in creating an interaction with their environment. In order to study preschool children's mathematical communication, this study was based on an ethnographic methodological traditions. 31 children’s mathematical communication was observed under 16 months. The results shows that preschool children are communicating mathematics through: linguistic representations, symbols and signs, linguistic tools and bodily expressions. Children communicate mathematically in situations when they are making comparisons about changes, and when they are trying to give descriptions about the world which surrounds them. It also shows that preschool routines, material support and activities stimulate mathematical communication. When teachers are supportive and engaged in children’s communication their mathematical knowledge can also be developed and deepened.