The authors examined the relationship between psychological strain, emotional dissonance and emotional job demands during a working day of 65 Dutch (military) police officers, using a 5-day diary design. We hypothesized that emotional dissonance partly mediated the relationship between psychological strain at the start and at the end of a work shift. We also tested the mediating role of emotional dissonance between emotional job demands and psychological strain at the end of a work shift. Results of structural equation modeling analyses showed that psychological strain at the start of a work shift had a positive effect on the experience of emotional dissonance and psychological strain at the end of a work shift. Emotional dissonance partly mediated the relationship between psychological strain at the start and psychological strain at the end of a work shift. Results are discussed in light of conservation of resources theory (Hobfoll, S. E. (1988). "The ecology of stress." New York: Hemisphere Publishing Corporation).