The measured thermal behavior of a massive building that uses passive techniques for indoor air conditioning is presented. The building thermal transient behavior was simulated with SIMEDIF code. The measured mean indoor temperatures fall between 20 and 23.5ºC, while the outdoor temperature is around 15ºC. Because of the symmetry of the building with respect to the north-south plane, the assumption that there is no heat flux between east and west wings has been made. Measured data set and simulated data set are both in good agreement. Thus, the assumed symmetry hypothesis was appropriated and the great potentiality of SIMEDIF code for transient simulation behavior was proved.