Carboxyl methyl cellulose (CMC) is one of the most commonly used theological modifiers for paper coating colors. Addition of CMC influences, among other things, the pore size distribution of coating layers which is an important parameter for paper coatings and affects the print quality and optical properties of the coated paper. In the present study, the effects of CMC on the pore size distribution of kaolin based coating layers applied on polyester film were investigated by means of H-2 and H-1 NMR relaxation methods. The pore size distributions of two types of coating layers, with or without CMC, were determined from the observed H-1 (at 26 MHz) and H-2 (at 4 MHz) NMR relaxation profiles of the imbibed water. The results showed that pore size distribution of the CMC-containing coating layer is significantly shifted to larger pore sizes compared to that of the coating layer without CMC. The results are also in good agreement with observations made by other methods. Furthermore the molecular dynamics of the imbibed water was studied in detail by measuring the average H-2 spin-lattice relaxation times at different resonance frequencies (4-30.72 MHz). H-2 quadrupole splittings were observed, which are dependent on the relative orientation between the coating layers and the applied external magnetic field.