The main objective of the present work is the elaboration of PU/MMT nanocomposites foams by the use of local “bentonite” called “ Maghnite”. These nanocomposites were elaborated by in situ polymerization. The first stage relates to the organophile treatment of the MMT by an alkylammonium C18H39N in order to increase the interfoliate distance. Whether fulfilled, the following tasks should be the optimization of the PUR formulation; the nanocomposites PU/MMT foams have been carried out by the processes of free expansion. The identification and characterization of the raw materials and the obtained foams have been done by various methods such as: FTIR, XRD, impact strength test, Test of inflammability. From the found results, it is assigned by XRD analysis that the interfoliate distance increases from 12.13 °A to 29.56 °A and the structure is fully exfoliated. We notice from impact strength and tenacity tests applied for these materials, that the generated mechanical properties are better than for those no modified. We assume the role played by the nanoclay as auto extinguish agent in order to improve the fire proof of elaborated PU/MMT nanocomposites.