This paper is about the application of active stack system to enhance natural ventilation inpublic housing in Singapore. About 86% of the population is staying in high-rise publichousing, known as Housing and Development Board (HDB) flats, which is designed fornatural ventilation. The main objective of this work is to assess the status of naturalventilation in a typical 4-room HDB flat using scaled model in the wind tunnel, and todevelop an effective active stack system to enhance natural ventilation in the flat. Fournumbers of stacks with different sizes were tested at two locations in the flat. The study showsthat the active stack leads to substantial increase in the air velocity at the room and thusmeeting the humans thermal comfort condition. It was noted that the velocities increasealong with the increase in the stack size. For smaller stacks, there is not much increase in theair velocity with the increase in fan speed.