Direct observations of the behavior of wild Japanese macaques (Macaca fuscata) in many populations have been recorded over the decades. However, novel behaviors continue to be reported. Here, I report a novel social behavior “rump-rump contact” among males of one group in Yakushima, a behavior that has not been reported in any macaque species. Eight cases of this behavior were observed in 87 observation-days between August and October 2018. They were classified into two types: the RR type, where the rumps of the two individuals symmetrically touched each other, and the RT type, where the rump of one individual was in touch with the lateral torso of the other. At the same time as this behavior, the two individuals clasped the other's body and touched the other's hindquarter by wagging tails. The contexts in which this behavior was observed suggests that it helps in regulating social tension, as might be the case in bonobos where the RR type is known. However, it is likely that this behavior in the two species is not entirely comparable, as no genital contacts with thrust was observed in the Japanese macaques as part of this behavior. In the macaque, it is possible that this behavior was derived from “presenting” because it was seen just before this behavior, and the same action of clasping the other's body was seen at the same time as this behavior. This is a highly novel behavior in that, wagging tails may be a kind of tactile communication, which has never been reported in nonhuman primates. Additionally, it is valuable that this behavior previously known only in bonobos and chimpanzees was also observed in the Japanese macaques, which have very different phylogenetic relationships and social systems. Further studies may reveal the affinitive relationships that goes beyond the strict dominance relationship between males.