The Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency (ESA), to be launched in November 2009, is aimed at retrieving soil moisture with an accuracy better than 0.04 [m3/m3] and with a temporal sampling better than 3 days. SMOS carries a fully polarimetric L-band (1.4 GHz) Microwave interferometer. The passive microwave observations are done at multiple view angles (between 0° - 55°), and with a spatial resolution ranging from 35 km at nadir about 50 km. Within the context of the SMOS Calibration / Validation activities, the Valencia Anchor Station experimental site, in Spain, was chosen to be one of the main test sites. It is a semiarid environment with low annual precipitation (around 400mm) and is characterized by an extensive network of measurements at different levels (both in the atmosphere and in the soil) in order to derive surface energy fluxes. The aim of this study is to give a first insight of the SMOS data over the VAS area (equivalent to a SMOS pixel). In order to help better understanding the exact signification of the SMOS signal, an evaluation of SMOS data is done through a comparison with ground data (Match-ups). Match ups are passive microwave brightness temperatures using the surface variables as well as the characteristics of the VAS area. In this framework, a coupled SVAT - radiative transfer model was developed for distributing soil moisture and the resulting microwave emissions. The hydrological processes are simulated with a SVAT (Soil-Vegetation-Atmosphere-Transfer) model named ISBA (Interactions between Soil Biosphere Atmosphere), while the microwave emission is simulated using the L-MEB (L-band Microwave Emission of the Biosphere) model which is part of SMOS Level 2 processor. This comparison with the first SMOS data is an important step into the validation of SMOS soil moisture retrieval algorithm.