There is a lack of studies analyzing the association between grandparental investment and grandparents' happiness. Using nationally representative data from the Generational Transmissions in Finland project (sample n = 2,152 older adults), this study explores (a) whether grandparenthood is associated with self‐evaluated happiness, (b) whether there is an association between grandparental investment (measured by contact frequencies with grandchildren) and a grandparent's self‐perceived happiness, and (c) whether differences in the associations between grandparental investment and happiness vary according to the gender and lineage of a grandparent. Our results show that just being a grandparent is not associated with self‐evaluated happiness among older Finns. However, a positive association was found in the case of maternal grandmothers' investment and happiness.