The present study investigates the differences in the dielectric properties of normal and cancerous tissues of human lungs in vitro to extract the characteristic parameters from impedance spectra and provide some reference data for the impedance measurement of human lung cancer in vitro. Specimens were obtained from operation patients with lung cancer. The impedance spectra of the specimens were measured from 100 Hz to 100 MHz. The air filling factor F is defined for describing pulmonary air content. The results show that the dielectric properties of normal tissue decrease with increasing F. The relative permittivity of cancerous tissue is 1.2-3 times larger than that of normal tissue with F = 0.1781. The conductivity of cancerous tissue is 1.6-2 times larger than that of normal tissue and there is a significant difference in their impedance spectra. The results show that the differences in the dielectric properties and impedance spectra of normal and cancerous tissues are significant, providing basic data for the impedance measurement of human lung cancer in vitro.