Grandparental involvement in childrearing has been associated with children's social-emotional development, yet findings are mixed. Grandparental involvement is a multidimensional concept that includes both quantity (i.e., the degree of grandparental involvement) and quality aspects (i.e., the quality of parent-grandparent coparenting and the quality of grandparenting practices). This study included both quantity and quality aspects to identify heterogeneous patterns of grandparental involvement and examined the associations between distinct patterns of grandparental involvement and children's social-emotional outcomes. Participants were 428 families with Chinese preschoolers (Mage = 53.75 months, SD = 10.32; 51.4% boys). Primary parental and grandparental caregivers completed the questionnaires. Four patterns of grandparental involvement emerged: the low-involvement mediocre-quality, the median, the high-involvement uneven-quality, and the high-involvement high-quality groups. Heterogeneous patterns of grandparental involvement exist and are differentially associated with children's social-emotional development. Children with grandparents in the high-involvement high-quality group demonstrated higher levels of social skills than those in the low-involvement mediocre-quality group and the high-involvement uneven-quality group. They also showed the lowest level of problem behaviors. This study highlights variations in grandparental involvement and helps to clarify previous inconsistent findings regarding the role of grandparental involvement in child development. (PsycInfo Database Record (c) 2024 APA, all rights reserved).