We synthesized a novel perovskite-type oxide, HgSnO3, under high pressure and high temperature, and investigated the crystal and electronic structures as well as the transport properties. It was found that HgSnO3 possesses a trigonal-hexagonal lattice with space group R (3) over barc. The band gap of HgSnO3 estimated by diffuse reflectance spectrum measurement is relatively small (1.6 eV), irrespective of the large octahedral tilting distortion. The small band gap is caused by the increase in the bandwidth of the conduction and valence bands due to mixing between the empty Hg 6s orbitals and the antibonding Sn 5s-O 2p states and the mixing between the filled Hg 5d orbitals and the O 2p states, respectively. The electronic resistivity, Seebeck coefficient, and Hall coefficient measurements indicate that as-synthesized HgSnO3 is an n-type semiconductor.