During cheese ripening, micro-organisms grow as immobilized colonies, metabolizing substrates present in the matrixwhich generate products triggered by enzymatic reactions. Local limitation rates of diffusion, either in the lipoproteicmatrix or in the cells clusters, can be responsible for modulation in the metabolic and enzymatic activities of microorganismsand thus for the final result quality.Mass transfer phenomena can depend on the microstructure of the cheese matrix, and/or on the characteristics of thesolutes (charge, size, hydrophobicity, etc.). Floury et al. (2012) recently showed the power and the potentiality of theFluorescence Recovery After Photobleaching (FRAP) technique to study mass transfer properties of fluorescent solutesin complex food matrices such as cheeses.In this work we investigated the migration of solutes of variable sizes, charges and shapes by FRAP in a model cheesematrix based on ultrafiltrated milk with controlled microstructural and textural properties. Structural parametersof the proteinic network such as fractal dimension, pore size and tortuosity have been elucidated by a combinationof macroscopic (rheology, permeability) and microscopic (CLSM, TEM) techniques. FITC-dextrans of differentmolecular weights [4 to 150 kDa] and FITC-labeled dairy proteins were chosen as models of migrating solutes.We observed a strong dependence of diffusion on solute size. The higher molecular weight FITC-labeled moleculeswere more retarded in the model cheese than the smaller molecules. The degree of obstruction depends on the size ofthe pores in the matrix compared with the size of the migrating solute.FRAP is a promising technique to explore the diffusion properties of solutes in complex media like cheese, in situ and ata microscopic scale. Quantifying the diffusion coefficient for different solutes and to link it to the structure of the matrixis an important step to understand cheese ripening mechanisms.