Two types of focusing strategies on body information have been proposed. One is maladaptive focusing, involving suppressing one's own body sensations and evaluating one's own performance, and the other is adaptive, involving focusing on one's own body sensations without suppressing or evaluating them. The present study revealed that the maladaptive focusing strategy decreased parasympathetic activity and enhanced following negative emotion. Additionally, we investigated the influence of a serotonin transporter gene polymorphism on the two types of emotion regulation. As a result, participants with SS alleles of the serotonin transporter gene showed more negative emotions in the maladaptive than in the adaptive focusing manipulation associated with reducing parasympathetic activity. In contrast, although participants with L alleles showed reduced parasympathetic activity in the maladaptive condition, no such differences were observed in subjective emotions between the conditions. These results are consistent with the evidence of greater emotion regulation ability in individuals with L alleles compared to those with S alleles.