Technologies of Indoor positioning are widely used in commercial applications in the modern society; among them, fingerprinting is the most utilized method. The main challenge in fingerprinting-based localization is the severe fluctuations of received signal strength (RSS). Due to the fluctuations, localization results are often unstable. Therefore, we propose to define membership functions based on the distribution of RSS with a technique of fuzzy logic; specifically, a fuzzy rule is defined with offline data. Finally, fingerprinting method can find out the localization efficiently. The result of experiment show that the new method is effective to increase the stability of localization.