The transport properties of TlxCr5Se8 pseudo-hollandite have been investigated, from 2K up to 800K. A semi-conducting behavior is observed from 200K down to 2K, with a transition observed at T ~ 43K, at the antiferromagnetic transition. Above 200K, small values of ρ are obtained, close to 10 mΩ.cm at 800K. The Seebeck coefficient continuously increases in this range of temperature, reaching 300microV/K at 800K. Moreover, the thermal conductivity of this low dimensional structure is small, leading to a figure of merit ZT = S2T/(ρκ) = 0.5 at 800K. All the electronic transport properties can be fitted by standard Boltzmann equation, with a large scattering parameter (r = 3/2, characteristic of diffusion by ionized impurities). The combination of small thermal conductivity, large scattering parameter and low concentration of carriers (4.5.1019cm-3) is at the origin of this large ZT.