Polycrystalline samples of Cu(3-x)Sn(x)Se3 were synthesized in the composition range x = 0.87-1.05. A compositionally induced evolvement from tetragonal via cubic to monoclinic crystal structures is observed, when the composition changes from a Cu-rich to a Sn-rich one. The Cu(3-x)Sn(x)Se3 materials show a metal-to-semiconductor transition with increasing x. Electronic transport properties are governed by the charge-carrier concentration which is well described by a linear dispersion-band model. The lattice component of the thermal conductivity is practically independent of x which is attributed to the opposite influence of the atomic ordering and the inhomogeneous distribution of the Cu-Se or Sn-Se bonds with different polarities in the crystal structure. The highest thermoelectric figure of merit ZT of 0.34 is achieved for x = 1.025 at 700 K.