The analysis of social calls emitted by bats in the Pipistrellus genus has played an important role in assessing cryptic diversity and in investigating reproductive strategies and foraging ecology of these vespertilionids. Our study deals with social call structure of a recently discovered species, Pipistrellus hanaki. Because it shares a common ancestor with P. pygmaeus, we hypothesized that as in the other species from this group social call structure in P. hanaki retains the basic design observed in other bats from the same genus. We also hypothesized that as in other pipistrelles such calls fulfill context-dependent functions, being used by both foraging and mating bats for different purposes. However, we found that these calls have a structure rather different from that seen in most pipistrelles. Two different types of multi-harmonic, broad-band and long-duration social calls were identified, with distinctive temporal structures. Single component, frequency modulated-quasi constant frequency (FM-QCF) calls were emitted during summer at foraging sites where feeding buzzes were regularly produced. In autumn, when feeding buzz rates decreased and males caught at recording sites had prominent testes, a second type of single or multi-component calls with a fluctuating frequency over time was more frequent. Unlike the typical multi-component social calls recorded in several Pipistrellus species, our results suggest that social calls used by foraging or mating P. hanaki have markedly different structures. Because social calls of bats are speciesspecific and may function in reproductive isolation, we hypothesize that differentiation of social calls in P. hanaki has been associated with the divergence of this species from P. pygmaeus.