In multilayered polymer films, the influence of thickness reduction on the glass transition temperature (T-g) and cooperatively rearranging region (CRR) size was investigated using temperature modulated differential scanning calorimetry (TMDSC). The materials used in this work are multilayered films comprising tens to thousands of alternating layers of two polymers, Bisphenol A Polycarbonate (PC) and polymethyl-methacrylate (PMMA) fabricated by layer multiplying coextrusion technique. The TMDSC measurements enable the calculation of the average values of CRR parameters at the dynamic glass transition temperature (T-g) using Donth's method. The molecular mobility in each polymer is found to be altered in entirely different ways as the thickness of each component became thinner than 125 nm, whereby the polymers exist as two dimensional layers under those conditions. PC exhibits a drastic decrease in cooperativity volume at the glass transition while slight modifications are observed for PMMA. These observations are discussed in regard with the role of the large interface amount between the two different polymers and the evolution of the macromolecule conformations. (C) 2012 Elsevier Ltd. All rights reserved.