In recent years, an increasing number of rural grandmothers in mainland China have migrated to cities for the sake of their grandchildren and to share the burden of childcare with their adult children. In childrearing cooperation, the rural-urban migrant grandmothers face not only intergenerational differences but also rural-urban differences in childrearing. When rural-urban grandmothers provide childrearing assistance in cities, their grandmothering is influenced by the urban childrearing discourse through their cooperation with urban parents. However, our knowledge about their grandmothering is limited. Moreover, existing studies on the migrant elderly tend to describe grandparents as having outdated values and being passively constrained by the structure; therefore, these studies have neglect their agency. In my research, I explore how rural-urban migrant grandmothers contribute to grandchildren's daily care, education and discipline under the influence of urban childrearing discourse, which is mainly reflected in their cooperation with their adult children. I will examine both the intergenerational solidarity and conflicts in the cooperation. Moreover, inspired by the concept of agency, I argue that rural-urban migrant grandmothers are strategic agents, and I examine their agency in response to the urban childrearing discourse. My qualitative data are obtained through in-depth interviews and participant observations with 20 rural-urban migrant grandmothers in two field sites--Beijing and Taian--on mainland China. I find that the cooperation mechanism reflects flexibility, diversity and dynamic. The rural-urban grandmothers use diverse methods to cooperate with their adult children and to contribute to grandchildren's daily care, education and discipline. To fulfil their tasks, grandmothers face challenges such as uncertainty, financial disadvantages, and educational disadvantages. Moreover, the grandmothers experience many different childrearing conflicts with the parents, such as consumption, nutrition and health care. However, grandmothers can actively respond to these challenges and use the strategies of constructing an alternative discourse, using alternative methods and learning to cope with the problems. To deal with the conflicts, grandmothers emphasise two narratives: family harmony, which is most important; and, all for the child. Based on these two narratives, grandmothers use different strategies, such as direct and indirect communication, using hidden strategies, compromising, and keeping silence, when helping their adult children during childcare. Located in the context where the family is regarded as a union and the intergenerational relationship is protected, the agency of rural-urban migrant grandmothers is solidarity-oriented and altruist-oriented agency.