The graduate thesis describes topic „Energy renovation in apartment building“. Apartment buildings are responsible for 40% of total energy consumption in Europe. They have grate potential for energy savings due to the high percentage of buildings with unsatisfactory thermal protection. Both in European Union and Republic of Croatia, energy efficiency of buildings becoming a priority that would reduce energy consumption and reduce environmental pollution. The main goal of graduate thesis is to show the importance of energy renovation of apartment buildings, to show the process of energy renovation of apartment buildings, energy audit and analysis before and after the implementation of two measures and presentation of savings after the implementation of two measures. The conclusion of graduate thesis is based on two measures to conclude the profitability of the measures after their implementation and return on investment.