The objective of this study was to investigate the effect of physical characteristics of different size classes of J. curcas seeds on shelling performance using a modified disc mill. The seeds were grouped into four size classes using sieves with hole diameters of 8, 9, 10 and 12 mm. Length, breadth, width, arithmetic and geometric diameter, bulk and solid density, and surface area were significantly different at p≤. 0.01. No significant differences were found in terms of sphericity and moisture content. Smaller seed size lead to higher porosity and percentage of shells. Rupture force was examined along length (L), width (W), and breadth (B) axes. A prototype of a disc mill was re-engineered and optimized. The preferential orientation of the seeds passing the mill was in the vertical direction. Optimum setting of rotational speed and aperture between the discs of the mill were strongly related to seed breadth. As the output fractions, dust, shells, fragmented kernels and full kernels could be separated pneumatically. Meanwhile, partially-shelled and unshelled seeds could only be separated manually by visual inspection. Under optimum conditions, the shelling efficiency for the four size classes was determined as 81.0, 83.5, 83.7, and 84.6%, respectively. Compared with results from unsorted seeds, pre-sorting the seeds significantly reduced the amount of partially-shelled and unshelled seeds at p≤. 0.01. The maximum capacity of the machine was estimated as 131.5. kg/h which resulted in the lowest energy consumption of 0.002. kWh/kg.