Environmental agency of Special Region of Yogyakarta has responsibility for controlling the population of water quality by doing Merti Kali Program. Merti Kali Program is an activity that has the meaning of maintaining, preserving, and taking care of the river. The purpose of this study was to determine how the social marketing of the Merti Kali Program was carried out by the Environment Agency of the Special Region of Yogyakarta in changing people's behavior to preserve the environment of the river in the 2017 Period. The study used a descriptive qualitative method by collecting data through in-depth interviews, documentation, and other supporting data. The results of this study found that the elements in social marketing are 4P + 2P (Product, Price, Place, Promotion + Partnership, Policy). The product in this study is the form of behavior change. Price is a form of effort that did to achieve the desired results. Place in this study is easily accessible to the target audience during the Merti Kali Program socialization and community service activities. The promotion activity in this study was through social media, print media and electronic media, besides the workshop activities before the Merti Kali Program was held. Partnership in collaboration with the Environment Agency of Special Region of Yogyakarta is the River Activist Forum. Policy in this study has various forms, namely in the form of a Presidential Regulation to a Regional Regulation that supports the Merti Kali Program. Kata Kunci : Social Marketing