Abstract: The objective of this study was to determine the mechanical properties such as poisson’s ratio and modulus of elasticity of two onion varieties. The compression test was applied on Banko and Yalova 12 onions by using the load-displacement measurement device at laboratory conditions. From the measured vertical forces and deformation, rupturing force, stress and energy, poisson’s ratio and modulus of elasticity of onions were determined. Results showed that the modulus of the elasticity of both onion varieties were the most affected from the storage period. Cracking energy increased with storage time. Due to firmness, onion gets weaker with the storage time, this double increases the cracking energy of the onion. Modulus of elasticity was decreased drastically from 6.54 to 1.35 MPa for Yalova 12 and similar drop was seen for Banko varieties, which was from 8.14 to 1.49 MPa. The poisson ratio was found between 0.15 and 0.44 for both onion varieties.