A kinetic study of the delignification of cedar wood during organosolv treatment using 1-butanol was conducted. The results revealed that the primary particles in the delignification were not wood chips, but the tracheid cell wall in the wood structure. In addition, the delignification proceeded from the lumen of the tracheid cell wall into the middle lamella, which suggests that the kinetic situation was similar to that in the unreacted-core model. The amount of delignification increased with reaction time, although the cellulose remained a solid with mesopores. These results indicate that delignification should proceed to produce pure cellulose layers. Therefore, delignification was analyzed using the unreacted-core model, which revealed that the rate-determining step was the diffusion of dissolved lignin molecules within the cellulose layer. The mesopore and lignin particle size were approximately 3-10 nm and 2.7-5.4 nm, respectively. This size relation predicted that the diffusion rate would be very low, which supported the result from the unreacted-core model analyses. Finally, the effective diffusion coefficient was calculated from unreacted-core model equations, and produced a value of 4.09 x 10(-19) m(2) s(-1), which was low and indicated that diffusion of the lignin molecules within the cellulose layer was the rate-determining step.