The present study investigated the role of cognitive complexity and motor activity created by the problem-solving tasks on preschoolers' dyadic cooperative play. Fifteen 5-6 years old dyads were video-observed in three problem-solving tasks designed to contrast different levels of cognitive complexity and motor difficulties. Cooperation was defined by dyadic joint actions and emotional exchanges during problem-solving tasks as well as children's interactions outside the tasks. A micro-analysis of children's behaviors was realized on 3 minutes of video-observation in each condition. Results showed that the more the problem-solving task created motor activities, the more the children produced dyadic joint actions and had longer emotional exchanges. They also interacted more frequently outside the task. No differences were found when the cognitive complexity of tasks were compared. These results were discussed within Walton's framework (1945) suggesting a link between motor expressivity and cognitive development.