Abstract: The launch of Tianwen 1 marks the brand-new stage of the deep space exploration of China, which calls for the foundation of planetary science education in China. In planetary science, the ionosphere is considered to be the region of an atmosphere where a significant number of free thermal electrons and ions exist. These electrons and ions are produced via ionization of the neutral particles both by extreme ultraviolet radiation from the Sun and by collisions with energetic particles that penetrate the atmosphere. The planetary ionosphere, where the matters and energies outside the planet exchanges with the planet itself, is extremely important to the planetary upper atmosphere and the surface environment. In this study, we briefly review the studies of Venusian and Martian ionospheres based on the measurements starting from last century to provide the basis for comparative studies on planetary ionospheres.