This study presents an energy signature method for analyzing thermal inertia of apartment building located in Stockholm using IDA ICE software. The method involves analyzing the building’s consumption of energy hourly and calculating the temperature change rate of the building’s thermal mass. The study aims to identify the relationship between the building’s thermal mass and its energy consumption and evaluate the effectiveness of energy efficient measures in reducing the energy consumption of the energy. The results of the analysis show that the thermal inertia of the building has great influence on buildings energy consumption. The study then evaluates several measures taken including changing in material and improving the insulation of the building envelope and reducing the U-value of the building envelope. The simulation results show that these changes could reduce consumption of energy in the building and energy signature method is a good and effective to use in these measures and results show promising outcomes. The study is effective using IDA ICE and identifies potential for measures in energy saving.