The office market is an interesting revelatory of territorial evolutions. In this perspective, the aim of the communication is to present how the evolutions of Belgian office markets are related to urban mutations. The Belgian situation clearly illustrates how office locations interfere with the urban hierarchy, with a very strong concentration of the office market activity in the Brussels region. Moreover, there is in Belgium a clear correlation between the position of the cities in the urban hierarchy and the size of their office stock. Even though, there are some exceptions to this general law, with weaker developments in the Walloon cities of industrial tradition and, on the opposite, larger stocks in the Flemish cities of Leuven and Mechelen. More than the local economic development, it is in fact the progressive integration of those cities in the Brussels metropolitan dynamics which explain this situation. Since the eighties, important office parks have been developed in the Belgian outskirts. Our treatments have showed that this evolution leads to a relative decline of the city centres office function. For instance, cadastral data on the rental values of the whole country have showed that the representation of the city centres of the main urban regions have decreased from 60% in 1993 to 53% in 2003. For Brussels, it is estimated that 15% of the stock is now positioned in out-of-town locations.