We fabricated Bi _0.98Sb _0.02 wires with diameters in the range between 200 nm and 2 μm and studied their electronic transport and thermoelectric properties. Rotational diagrams and strong Shubnikov-de Haas oscillations show that the wires have a high degree of crystallinity. The temperature dependence of the resistance evidences a semimetal-semiconductor transition at a critical diameter of roughly 300 nm. Our BiSb nanowire samples feature both electrons and holes that contribute to negative and positive thermopower, respectively; we find evidence of the interplay between the two types of carriers according to wire diameter and temperature. An evaluation of the power factor, and of its dependence on wire diameter, temperature, and the magnitude and direction of the magnetic field, is presented.