In the present work was carried out the surface modification of microfibril and cellulose whiskers. Two different techniques were tested, one of them was the liquid phase modification and the other one, gas phase modification. Five reactants were tested, palmitoyl chloride, acetyl chloride, sebacoyl chloride and two anhydrides allow to functionalize the surface of the cellulose, granting it the hydrophobic character required. The liquid phase modification was made just with palmitoyl chloride, to perform this reaction was hard to find the conditions (not available information, no previous work) and many things to do to carry out the reaction, one of that was the exchange of solvent, from water to DMF; residual water and the size of the particles was the parameter to help to decide whether the exchange had worked. From the results we can say that the right temperature to accomplish this type of modification is 90 ° C and the time can change between 24 and 96hours, always taking care of the amount of pyridine to add. The gas phase modification was made with the five reactants, in all cases (except with maleic anhidride) the cellulose was modified. Was possible to find two reactants that just modify the surface of the crystal, sebacoyl chloride and ASA anhidride, the last one is environmentally friendly; in these cases the DSg was lower than DSsurface.