In this work, the biosorption mechanism of the cationic dye Methylene Blue (MB) on natural White Pine sawdust (NS) (Pinus durangensis) was investigated. Likewise, the surface charge distribution of NS was determined, and its point of zero charge was found to be 4.3. Besides, the capacity of the NS for adsorbing MB was increased 1.7, 2.0 and 4.6 times when the pH was raised from 3 to 4.25, 3 to 7 and 3 to 10, respectively. This behavior was attributed to the electrostatic attraction between the negatively charged surface of NS and the cationic species MB+. The adsorption capacity increased with increased temperature because the adsorption was an endothermic process. The adsorption capacity was drastically reduced by increasing the ionic strength of the solution corroborating with the fact that the electrostatic attractions played a crucial role in the adsorption of MB on NS. It was also shown that the MB was chemisorbed because the adsorption was not reversible. The predominant adsorption mechanisms were the electrostatic attraction and chemisorption and not ion exchange