Technical Abstract: Milling is a key process to soften leather for adequate compliance. It is, however, still not well understood for its effects on the leather structure and mechanical properties. To consistently produce high quality leather, it is essential that the tanner understands the impact and effects of every mechanical operation in the leather-making process. This investigation is devoted to gain a better understanding of its effects on pliability and some other properties concerned by the leather industry, such as mechanical strength and toughness. Observation showed milling leads to a decrease in Young's modulus, consequently an improved compliance and softness. Data, however, also showed little change in tensile strength and toughness. Moreover, leather products in service are constantly being stretched. For understanding the mechanical behavior of leather products under cyclic stretching, we measured the energy loss (hysteresis) during the cyclic tensile tests using an advanced computing program. Data showed that hysteresis is the greatest for the first cycle; thereafter, the rest of hysteresis values are relatively unchanged. We also discovered that drum milling significantly decreases the hysteresis. This implies a structural change occurs during milling, resulting in a removal of the residual stress that was introduced during the leather making process.