Drawing on Conservation of Resources theory, this study examines the curvilinear relationships between work passion and organizational citizenship behavior (OCB) as well as the moderating effect of collectivistic values. Using 233 paired supervisor-employee responses from Russia, I found that harmonious work passion and OCB are positively related up to a point, after which higher levels of harmonious work passion are associated with declining OCB. The main curvilinear effect of obsessive work passion on OCB was not significant. Collectivistic values were found to significantly interact with obsessive work passion but not harmonious work passion in the way they affect OCB. Employees with intermediate levels of obsessive passion who score high on collectivistic values tend to engage more in OCB than those who score low on collectivistic values. Interestingly, at low levels of collectivism, the inverted U-shaped curve that illustrates the relations between obsessive passion and OCB changes into a U-shaped curve, suggesting that the highest engagement in OCB will be no longer observed at intermediate levels of obsessive work passion but rather at the lowest and highest levels of obsessive work passion. The findings contribute to work passion research and suggest that curvilinear rather than linear relationships may exist between work passion and its outcomes, which may account for the existing inconsistencies in previous studies in regards to either positive or negative work passion‒outcomes relationships.