Older employees are not only confronted with subtle negative stereotypes about cognitive decline, but they also tend to internalize these negative stereotypes (i.e., they agree with the idea that intellectual performance declines in old age and they feel affected by this decline). Previous research has shown that internalizing negative age stereotypes has detrimental effects on work-related outcomes. Little is known about how internalized negative stereotypes shape older employees’ social emotions and social motivation. In the present research, we argue that older adults who internalize negative age stereotypes feel insecure about their belongingness in the workplace and this has negative motivational consequences. Four out of five studies and an aggregate analysis with a total of N = 1,306 older employees (age 50–76 years) supported this hypothesis. Internalized age stereotypes were negatively related to social approach motivation toward coworkers through reduced sense of belonging in the workplace and low positive affect. In addition, internalized age stereotypes were positively related to social avoidance motivation. Investigations of the causality of these relationships revealed mixed results. We discuss these findings from the perspective of socioemotional aging and the need to belong. In sum, the present research adds to knowledge on the role of internalized negative stereotypes for older employees’ social lives and, potentially, their success in the work domain.