The main objective and novelty of this study is to investigate the effect of particle size and alkali treatment on physical, mechanical properties of tamarind pod shell (TPS)‐reinforced epoxy composites. The treated and untreated composites were fabricated with different particle sizes with TPS content of 10 wt%. The mechanical, physical, and morphological properties of specimens were investigated. It was revealed that the density and mechanical properties of the treated and untreated composites increased with the decrease in the particle size; whereas, the water absorption percentage and void content decreased for the same. The treated composite with the particle size of 75 μm exhibited the maximum tensile, flexural, and compressive strength. Further, the multiscale finite element (FE) model was developed using the Digimat‐FE software to simulate the tensile behavior of composites with different particle size. The simulation results revealed that the stress concentration level was more in the vicinity of the voids, and the higher stress concentration was observed in the matrix phase with the increase in particle size. Also, it was found that the predicted results from the multiscale FE model showed a good agreement with the experimental results. The results suggested that the TPS filled epoxy composites have potential utility in the fields of automotive interior panels, particulate board panels, household goods, packaging materials, building partitions, and many other applications.