Healthy buildings may lose their healthy characteristics over time and due to changing circumstances during their usage phase, which may lead to biological and psychological health problems for their users. Thus a process model is required for buildings which ensures that the initial healthy environment is retained. This study therefore introduces a conceptual Process Model for the Sustainability of a Healthy Building. In the study, the sustainability of the healthy building and its criteria were determined by the help of the definition of sustainability and associated criteria. Then, the changes which prevent the building from sustaining its healthy status were introduced. Based on the events that lead to the loss of healthy building performance, the actions and functioning of the process model were created. Action steps were then composed and the relationship between these steps were established. As a result, the principal components of this model are determined as Achievement of a Healthy Building, Sustainability Assessment of a Healthy Building, and Sustainability Management of a Healthy Building. Application of the procedures in the proposed model can help maintain the healthy characteristics of buildings throughout their operational lifespan, thereby preserving the basic requirement for a healthy environment.