Employees develop global perceptions regarding the extent to which their work organization cares about their well-being and values their contributions, which is known as perceived organizational support (POS). While the extant literature on POS is vast, a majority of the research has been cross-sectional in nature, which ignores potentially important within-person variation in the job attitude. In addition, much of the research on POS has not directly investigated the role of affect in relation to POS, despite POS connoting caring by the organization. The current study explores the extent to which POS fluctuates on a short-term basis as a result of emotional reactions to events that employees experience at work. In addition, it integrates Affective Events Theory to understand the role of affective events and their associated transient discrete emotions in explaining why POS may fluctuate, and whether that relationship depends on the strength of individuals’ socioemotional needs. To test my hypotheses, I employed a diary-study method in which 56 working adults responded to three surveys per day for ten days. The results suggest that while POS is relatively stable job attitude, it fluctuates over the course of two weeks. I also found that the events that employees experience at work are significantly related to both happiness/joy and anger (discrete emotions). In turn, both happiness/joy and anger are significantly related to POS These results advance organizational support theory by highlighting the role of affect in relation to POS and illustrating that momentary changes in affect relate to momentary changes in POS. Furthermore, only one socioemotional need moderated the relationship between discrete emotions and POS. Organizations can use the results of the current study as evidence for the importance of providing signals of POS in socialization processes for new employees, as it seems that once POS develops, it is relatively stable.