The increasing popularity of indoor localization systems brings the need of providing energy and cost-efficient service. Currently, we are developing the fingerprint-based indoor localization system using IEEE 802.15.4 named FILS15.4. It uses a small transmitter powered by a coin battery, limits the detection resolution by one room, allocates several receivers on the field, and assigns multiple fingerprints using the parameter optimization method. It has been evaluated only for one-floor environments. This paper investigates the applicability of FILS15.4 in a two-floors environment of the #2 Engineering Building in Okayama University. The receivers allocated on both floors are used together for localization. The experiment results confirm sufficient detection accuracy.