Pyrolysis of biomass pellets is a complex process that is generally influenced by internal transport limitations. For the better understanding of these effects, a rigorous fully transient 1-D mathematical model for a single pellet was developed that includes unsteady state mass and energy conservation equations for gaseous and solid species. The heat transfer within the pellet is mainly due to conduction whereas, convection and radiation play a significant role in the heat exchange between the pellet surface and the reactor wall. The model involves set of partial differential equations which can be solved for two different cases viz. a reactor with constant wall temperature and a non-isothermal reactor wall with constant heating rate. The formulated equations are solved using MATLAB by converting them into a set of algebraic equations using discretization technique. The resistances due to transport limitations within the pellet are quantified in terms of effectiveness factor. The effectiveness factor was found to be dependent on pyrolysis heating policy, pellet thickness, and thermal conductivity.