The measurement of effective diffusivity for KD306 sulfur-tolerant methanation catalyst has been carried out using the 'single pellet string reactor' technique. The average tortuosity factor for KD306 catalyst was experimentally determined to be 7.2. The results of linearization method are in good agreement with the solutions of the parameter estimation method, which shows that the assumptions made in linearity processing are reasonable, and that the methods of Linearization and parameter estimation can both be used to determine effective diffusivity efficiently.