In this study, we exclusively found that the exfoliated poly(vinyl acetate)montmorillonite (PVAc-MMT) nanocomposite latices could be straightforwardly fabricated by soap-free emulsion polymerization and cast into a film. The as-fabricated films were transparent with the exfoliated MMT nanoplatelets in flat form uniformly dispersed in the PVAc matrix. Certain bonding of PVAc matrix to the exfoliated MMT nanoplatlets refrained it from removal by acetone in Soxhlet extraction. Exfoliated MMT nanoplatlets (10 wt %) in the film was able to reduce the water vapor permeability coefficient to only 9% that of the neat PVAc. According to the generalized Nielsen's permeability model for the composites containing impermeable fillers in sheet form, the average aspect ratio of exfoliated MMT platelets was calculated as 327, similar to those directly estimated by atomic force microscopy and transmission electron microscopy. (c) 2007 Wiley Periodicals, Inc.