The prospect of exhaustion of fossil fuels and climate change caused due to the extreme use of fossil fuel consequence shifting energy supply from fossil energy to renewable energy. India ranks the second-largest producer of agricultural products and generates huge quantities of agricultural crop residues. These agricultural residues are a promising source of energy producing components. The goal of the present investigation is to study the effect of biomass particle size and devolatilization temperature varied from 500 degrees C to 800 degrees C on pore size distribution, pore volume, surface area, surface morphology, and a structural parameter of the biomass char. The Scanning Electron Microscope images results reveal the variations in the surface morphology of coconut fiber and sugarcane bagasse biomass chars and the decreases of pore fractions with an increase in temperature. Biomass char samples are mesoporous and microporous in nature confirmed by Barrett, Joyner, and Halenda (BJH) analysis, pore size ranging from 25 to 350 angstrom for mesoporous and 1.0 to 20 angstrom for microporous particles with open-ended adsorption-desorption isotherms and a substantial increase in BET surface area was observed at all the varied temperatures. A polynomial regression approach is adopted to find a relation between the pore volumes and pore size using thickness plot data to calculate the structural parameter. The structural parameter is a factor which predicts the behavior of Random Pore Model for char combustion kinetics. If the structural parameter is large then the model will result in a maximum reaction rate as the reaction proceeds, due to the growth of the size of the cylindrical pore causes an increase in the available surface area for reaction and results in an increase in the rate of reaction. Finally, as the reaction proceeds due to more pores interaction and pores overlapping, the available surface area decreases and therefore the rate decreases as the structural parameter value is smaller. The structural parameter estimated for mesopore size and micropore size ranges between 6.0 and 18.0 for Sugarcane Bagasse and 7.0 and 17.0 for coconut fiber particles.