Recent evidence reveals that transportation’s improvements within metropolitan areas have a clear effect on population and job decentralization processes. Yet, very little has been said on how these improvements affect the spatial organization of the economic activity in the suburbs. This paper analyses the effects of transportation’s changes on employment subcenters formation. Using data from metropolitan Paris between 1968 and 2010, we first show that rail network improvements cause the expected job decentralization by attracting jobs to suburban municipalities. Our main contribution is to show that the new rail transit clearly affects the spatial organization of employment through the number and size of the employment subcenters: not only does the presence of a rail station increase the probability of a suburban municipality of belonging to a subcenter by 5 to 10 %, but a 10 % increase in municipality proximity to a suburban station is found to increase its chance to be part of a subcenter by 3 to 5 %.