[en] Radioactive laboratory will be used for thorium extraction and purification process before can be used as a nuclear fuel for generating electricity in nuclear power plant. One of the criteria for laboratory is pressure inside shall be negative pressure relative to adjacent room or surrounding area. The objective of this research is to design the heating, ventilation and air conditioning (HVAC) system with negative pressure for radioactive laboratory to ensure the thorium extraction and purification process can be done safely without causing danger to human and environment. The output of this research is important to ensure all the activities done in radioactive laboratory followed safety, security and safeguard guideline as recommended by International Atomic Energy Agency (IAEA). (author)