Ventilation is essential to maintain a healthy indoor environment. However, in summer and winter, thermal conditions of outdoor air are so poor that ventilation cannot but increase energy consumption. Thus, energy-efficient ventilation system is very important to reduce energy consumption. Thermal labyrinth ventilation system (TLVS) is a ventilation system which intakes outdoor air through an underground concrete structure shaped like a labyrinth. By the heat exchange with ground, this system can pre-cool and pre-heat the outdoor air in summer and winter, respectively. The aim of this study is to analyze the annual energy performance of thermal labyrinth ventilation system, applied to the E University building recently built in Seoul using measured data. As results, the annual maximum and average cooling effects on the outdoor air were 11.2(in July) and 3.2 Celsius, respectively, and the annual maximum and average heating effects were 24.8(in December) and 6.9 Celsius, respectively. The annual average dehumidification and humidification effects on the outdoor air were 1.8 and 0.8 gw/kgda, respectively. Taking into account the flow rates of the intake air to the air conditioners, the annual average outdoor air cooling, heating, dehumidification and humidification rates of the TLVS were estimated to be 17.5, 22.5, 15.6, 10.0 kW, respectively.