Single phase $Zn_4Sb_3$ with $98.5\%$ of theoretical density was successfully produced by direct hot pressing of elemental powders containing $1.2 at\%$ excess Zn for compensating the evaporation during the process. Temperature dependences of thermoelectric properties were investigated from 4 K to 300 K. Seebeck coefficient, electrical conductivity, thermal conductivity as well as thermoelectric figure of merit showed the discontinuity in variation at 242K, indicating the $alpha-eta$, phase transformation. Interestingly, it was found that lattice thermal conductivity by phonons is dominant in total thermal conductivity of $alpha-eta$. Therefore, it is expected that thermoelectric properties can be improved by reduction of lattice thermal conductivity inducing lattice scattering centers by doping and solid solution.