In pursuit of more creative and imaginative citizens, the Chinese Ministry of Education has launched policies and curriculum guidelines to promote play-based science learning. However, little research has been directed towards Chinese children's agency in play-based science activity settings. Informed by a cultural-historical conception of play, this paper examines how children's agency in science learning improved after the Conceptual PlayWorld implementation. Conceptual PlayWorld as an intervention in this educational experiment framed a larger study of two teachers interacting with 34 children (aged four to five years; mean age of 4.65 years) in group learning activities. 40.38 h of video observations, 5.75 h of child interviews and 1 h of teacher interviews were generated in total. The findings indicate that a Conceptual PlayWorld allows children to obtain some degrees of freedom and co-construct rules in the play-based science activity setting, which promotes children's initiatives and thereby their agency. In addition, children's active involvement in Conceptual PlayWorld activity settings motivates them to solve conceptual problems as responsible and intentional members, which also promotes their agency. We argue that a Conceptual PlayWorld in Chinese kindergartens appears to promote children's agency in science learning and can contribute to an active and creative citizenship.