Pairing and physical confrontation in adult sows causes social stress reactions and aggressive behaviors. Recently, maternal pig skin secretions were isolated and a mixture containing several fatty acids, now called pig appeasing pheromone (PAP), was synthesized. In this study, we investigated the effects of PAP on social and immune stress response in adult female miniature pigs. PAP or vehicle solvents were sprayed into the pens of individually housed adult sows. A two-week exposure to the pheromone did not alter basal salivary cortisol levels or circadian rhythms. Following this treatment, the animals were paired and placed in a new pen that was divided with a wire-mesh fence. Although salivary cortisol increased markedly in the vehicle-treated group, the PAP-treated group exhibited a drastic inhibition of cortisol secretion. This effect was sustained even after they were allowed to physically interact following fence removal. Moreover, the latency time of agonistic behaviors, such as escaping or biting, was significantly extended after PAP exposure. When lipopolysaccharide was injected intramuscularly, cortisol levels, rectal temperatures, and lying time lengths increased substantially. No differences were observed between the pheromone-treated and untreated groups. These results suggest that this synthetic pheromone alleviates social stress in adult pigs, although it does not affect immune stress responses. Our findings demonstrate the potential benefit of this pheromone in field applications and clinical disciplines relating to adult female pigs.