The range of materials in nanoscience is always the center of attention of the current materials research in materials properties enhancement as well as in the different types of applications. AB2O4 type spinel metal ferrites in the nano range is also very useful in numerous applications such as gas sensing, humidity sensing, wastewater management, catalysis, adsorption, and photo-catalysis, as magnetic nano-carriers for biomedical and energy applications, etc. Out of a number of applications, the present chapter is focused on the use of spinel nano-ferrites in humidity sensors. Efforts are focused on the basic understanding of the spinel nano-ferrites, humidity sensors, and detailed discussion on the spinel nano-ferrites humidity sensors. As per the possible humidity sensing applications of these spinel nano-ferrites, it may be highly useful in the future requirements of humanity.