This paper performs a field experiment to verify the availability of the proposed floor estimation algorithm for determining of mobile target in multi-storey buildings. The proposed algorithm is based on the use of Received Signal Strength Indicator (RSSI) obtained from Android smartphone which is simple and can be performed in a smartphone quickly. Besides, due to the dramatic increasing number of AP in a building, the test environment has huge number of AP been installed. The proposed algorithm has the capability of adopting the change of AP presenting to the mobile target and AP's signal variation. Experiment results show it get almost 100% accuracy in corridor and center region, but with much lower accuracy in the staircase area because there is not significant of strong enough RSSI there.