Crystals of CoSb3 were grown using the vertical Bridgman method at growth rates that varied from 0.4 to 2.8 mm/h. Thermoelectric properties were analyzed for both as-grown and post-annealed samples. Polycrystalline CoSb3 surrounded by Sb was obtained. Samples grown at the rate of 0.4 mm/h had larger CoSb3 grains than samples grown at the 2.8 mm/h rate. For the as-grown samples, the Seebeck coefficient was smaller than 200 μ/K, which is a nominal value [1–3]. The presence of residual Sb resulted in a decrease in the Seebeck coefficient and an increase in the samples' electrical conductivity. A subsequent heat treatment at 800 °C for 20 h eliminated the residual Sb, resulting in a significant increase in the Seebeck coefficients (ranging from > 200 μV/K) in the annealed samples, as compared with the as-grown samples. The samples with a higher growth rate had larger Seebeck coefficients of ∼500 μ/K after annealing.