Ventilation is essential to maintain a healthy indoor environment. However, in winter and summer, thermal conditions of outdoor air are so poor that ventilation cannot but increase energy consumption. Thus, energy-efficient ventilation system is very important. Thermal labyrinth system 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 preheat and precool the outdoor air in winter and summer, respectively. The aim of this study is to analyze the energy efficiency of thermal labyrinth system, applied to the Ewha University building recently built in Seoul, in winter and spring (from Dec. 1 to May 31). As results, it was found that average heating and humidifying effects in Jan. are $13.3^{circ}C$ and $0.3g_w/kg_{da}$ (41.96kW and 2.58kW), respectively, and average cooling and dehumidifying effects of thermal labyrinth system in May are $3.2^{circ}C$ and $0.7g_w/kg_{da}$ (22.97kW and 10.63kW), respectively. Total outdoor air sensible and latent, heating and cooling load was found to be reduced by 29.0% through the thermal labyrinth system in winter and by 25.8% in spring.