Nuts of Yalova-3 walnut (Juglans regia L.) variety were compressed with a universal testing machine. Force, energy and specific deformation before initial rupturing and kernel extraction quality were investigated as functions of shell thickness and geometric mean diameter at different compression positions (length, width and suture). Results showed that while energy for initial rupturing increased linearly with increase in shell thickness except for length position, it decreased linearly with an increase in geometric mean diameter. The direction of change of specific deformation as a function of shell thickness and geometric mean diameter was similar to that of energy for all compression positions. Regression analysis of the data on kernel extraction quality versus shell thickness and geometric mean diameter resulted in values for the coefficient of determination R-2 ranging from 0.12 to 0.73. Experimental results from compression tests indicated that cracking nuts at the length position required less force and yielded the best kernel extraction quality. (C) 2003 Silsoc Research Institute. All rights reserved Published by Elsevier Ltd.