The environmental impact of our current consumption pattern on the earth is growing. The linear economy is accelerating the environment pollution and increasing the use of resources. If we want to be able to gradually move towards a circular system it is vital to include in this strategy the way products are being cared for, which is Product care. Product care is an approach to use a product as a means to catalyze consumers’ care behaviour change. It does so in a user-in-control way (you wash your coffee machine regularly without any reminder), but also in a product-in-control way (the coffee machine will stop working if you don’t wash it on time). The control degree of the product care means the degree of consumer autonomy over product care behavior and the degree of product intervention on the user. This project is aiming to explore what is the optimal balance between these two ways when they design for product care. This goal is reached by using the research-through-design approach. In this study, three strategies of product care with different control degrees were formulated through analyzing and combining existing strategies from circular design and behavioral change design fields. Based on three strategies, six concepts were generated to test which strategies and control degree are most effective. And the result was that users preferred the concept of a balanced product care agency. To verify and further define the optimal balance between user in control and product in control, the control degree mechanism of product care was formulated which includes 3 aspects, 7 themes and 15 design elements. The mechanism can be used to help the designers to determine the agency of the dominant product care in the concept by determining the control degree of the design elements contained in the concept, which has been validated by the second user test. Besides, at the end of the project, the most effective and user’s preferred scope of balance between user control and product agency in the mechanism are provided: Awareness (The design intervention increases the awareness of product care and helps users to start care activities consciously.)：Balanced or more user-oriented Support (The design intervention supports the user in the process of product care, making care activities cognitively or behaviorally clearer and simpler.): Balanced or more product-oriented Feedback(The design intervention will give users feedback when they complete or fail to complete their product care activities.): Balanced