The objective of this work is to design and implement a fuzzy controller for naturally ventilated buildings. The controller is implemented in a test room using MATLAB™. Initially the controller was validated using simulated data. Simulations were carefully designed to allow simultaneous comparison of different controllers performances. Validation of the controller is performed in the test room by measuring the temperature distribution inside the room with no control action. The data are then compared to the open loop test results of the controller. The results illustrate that the fuzzy controller is capable of providing thermal comfort inside the room. (c) Elsevier