Technical Abstract: Edible films and coatings in foods can be used to increase shelf-life and improve organoleptic characteristics of foods by avoiding deterioration of food components and therefore promoting preservation of the final product. This study is the first to investigate the use of different size fillers for the purpose of preparing edible composite films with fillers less than 1.0 u in size. For this purpose, water vapor permeability and mechanical properties of HPMC (Hydroxy Propyl Methyl Cellulose) based films with the inclusion of different size MCC (Micro Crystalline Cellulose) fillers were studied. The water vapor permeability of the control HPMC film was 1.2 +/- 0.2 g-mm/kPa-h-m2 and did not show a significant change with the addition of fillers. A comparison of mechanical properties of the films with a tensile test showed that tensile strength of the control film, which was prepared using a 3 wt % HPMC solution increased from 29.7 +/- 1.6 MPa to 70.1 +/- 7.9 MPa with the addition of 500 nm size particles, while it increased only to 37.4 +/- 5.5 MPa with the addition of 3 um size particles. Also important is that the elongation percentage of the control film did not decrease significantly with the addition of sub-micron size fillers to the HPMC films. This study showed that the increased surface area per weight of smaller size MCC fillers compared to their larger size counterparts was highly beneficial in terms of film mechanical property improvement.