The development of thermoelectric (TE) materials is the key to reduce the use of fossil fuels because they can reuse waste heat to generate electricity via the Seebeck effect. One of the promising p-type TE materials is β-Zn4Sb3 which exhibits high TE efficiency. To further improve its TE efficiency, β-Zn4Sb3 samples have been prepared by melting and subsequently heating them for different heating time. For the heating time below 150 h, intercalation of Zn atoms into the Zn interstitial (Zni) site of β-Zn4Sb3 occurs. In addition, the amount of Zn and Zn3Sb2 secondary phases decreases, yielding crack-free β-Zn4Sb3 samples. For the heating time above 150 h, deintercalation of Zn atoms from the Zni site of β-Zn4Sb3 occurs. Here, we discuss the evolution of the microstructure and the electronic transport properties, electrical conductivity and Seebeck coefficient (thermopower), during heating from the viewpoint of the Zn intercalation and deintercalation, and this enables us to propose an optimal condition for preparing β-Zn4Sb3 with high TE efficiency.