A single crystalline Bi1.75Sb0.25Te2.02 nanowire of 250 nm in diameter was grown from a Bi1.5Sb0.5Te3 film via the thermal annealing method. The growth direction along [110] and the stoichiometric composition of Bi1.75Sb0.25Te2.02 for this nanowire were confirmed by the TEM results, and the layered morphology of the a-b plane was clearly observed by AFM and SEM. The self-heating 3ω technique was employed to characterize the thermal conductivity of this nanowire. The result shows that the thermal conductivity increases from 0.5 W/m-K at 10 K to 1.2 W/m-K at 120 K, then followed by a slight increase to 1.4 W/m-K at 300 K. It is observed that the low-temperature thermal conductivity of bismuth-antimony-telluride nanowire at 20 K is about six times lower than that of its bulk counterpart. The enormous reduction on thermal conductivity is mainly attributed to the enhanced phonon-boundary scattering of the nanometer size effect. In addition, the electrical resistivity and Seebeck coefficient were also simultaneously measured by the heater and electrodes built in the platform.