The effects of Sn-deficiency on the thermoelectric properties of polycrystalline Sni(1-x)Se (x = 0, 0.01, 0.02, and 0.04) compounds were investigated. The Sn-deficiency caused the formation of the SnSe2 secondary phase in the compounds, and the charge and thermal transport properties were affected significantly by the secondary phase. Although the Sn-deficient compounds exhibited higher thermal conductivities than stoichiometric compound due to its high thermal conductivity of SnSe2, significantly improved power factors led to the enhancement of ZT. The highest ZT of 0.61 at 848 K was achieved in Sn0.98Se compound, and detailed effects of SnSe2 on the enhancement were discussed. (C) 2017 Elsevier B.V. All rights reserved.