This research is a comparative study of Finnish and Australian science curricula in early childhood education (EC). The study aims to figure out the constructivist components of the science curriculum in two countries as well as locate the similarities and differences in the rationale and aims, contents, learning outcomes, learning activities, teacher’s role and assessment. The curriculum analysis framework developed by Van den Akker (2003) was used as a methodological framework for the curricula analysis. Based on the theory-driven content analyses, findings show that both countries have several components of constructivist curriculum, but not always clearly focused on science education. The Australian Early Years Learning Framework (EYLF) integrates children’s science learning within their five specific learning outcomes, whereas the Finnish national core curriculum for early childhood education and care has no defined learning outcomes in general. The Finnish curriculum more clearly than EYLF encompasses science and environmental education as a learning domain, within which children participate in targeted scientific activities to gain procedural knowledge in specific environmental-related concepts. More focus should be turned to the teachers’ role and assessment, which are not determined in science context in both countries. This international comparative study calls for the need of a considered EC curriculum framework that more explicitly has science domains with specifically defined rationale, aims, content areas, learning outcomes and assessment criteria. The implications lie in providing early childhood educators with tangible and theoretically solid curriculum framework and resources in order to foster scientific thinking in young children.