Nowadays, indoor positioning systems (IPS) have gained popularity for offering location-based services. Previously, we have proposed the fingerprint-based indoor positioning system using IEEE 802.15.4. By limiting the positioning resolution by one room, it can detect the current position accurately. However, this detection was only performed at one time, thus the accuracy has not been observed. In this paper, we present experimental evaluations of the implemented system when it runs for a long time on two floors with 15 rooms of #2 Engineering Building in Okayama University. The results show that it achieves 93.41% and 91.83% average accuracy of the correct room detection on each floor.