Biomass plays an important role in meeting the increasing global energy demand. Naturally grown grass and tree leaves are abundant and provide an inexpensive source of biomass. The handling and transportation of collected leaves and harvested grass are difficult because they are loose and have inconsistent structures. The objective of this study was to investigate the mechanical and thermal characteristics of briquettes produced from grass and three leaves. In this research, grass and tree leaves were dried, chopped, mixed with binder, and briquetted under pressures of 3, 5, and 6 tons/cm2, followed by carbonization at 600 °C for an hour to investigate their mechanical and thermal properties. The effects of compaction/briquetting loads on density, durability, and ignition temperature were analyzed for both non-carbonized and carbonized grass and leaf briquettes. The average densities obtained under 3, 5, and 6 tons/cm2 compaction loads were 919.8, 934.9, and 945.5 kg/m3 for grass briquettes, and 1102.7, 1117.0, and 1123.0 kg/m3 for leaf briquettes, respectively. Ignition temperature tests showed that the average ignition temperatures were 259.0, 272.3 and 277.7 °C for grass briquettes and 252.0, 266.7 and 273.7 °C for leaf briquettes. In the case of carbonized briquettes, the average ignition temperatures were slightly increased due to the lack of gas and liquid compounds after carbonization. Based on the analysis of compression tests obtained under 3, 5, and 6 tons/cm2, residual strengths were 16.2, 16.8, and 19.2 MPa for grass briquettes, and 13.7, 18.6, and 20.0 MPa for leaf briquettes, respectively. Test results indicated that both grass and tree leaves provided excellent mechanical and thermal properties, which can be used in a number of different industrial applications.