Biomass has an enormous potential to be used as an alternative energy source. As compared to other renewable energy sources such as wind, solar, and hydro, biomass gives CO2 and H2 which are mainly used to produce biofuel. The present work provides the details of numerical investigation of Neem and Ashoka leaves as a biomass feedstock for fixed-bed downdraft gasifier to produce Syngas. This work focuses on selection criteria and evaluation of thermochemical characterization of Neem and Ashoka leaves respectively.In the downdraft gasifier, biomass undergoes a series of processes such as drying in the drying zone, pyrolysis in the pyrolysis zone, combustion in the combustion zone, and gasification in the reduction zone respectively and get converted into a mixture of gases along with char at the bottom of gasifier. This gaseous mixture contains CO, CO2, H2O, H2, CH4, and higher hydrocarbon. The study concludes that both Neem and Ashoka leaves was having a high potential to be used as biomass for producing syngas which was proved to be a sustainable and eco-friendly source of energy.