There is an increasing need to understand the mechanical properties of human orbital fat and its encapsulating connective tissue (OFCT), but such knowledge is not available in the current literature. The purpose of the present study is to examine the mechanical properties of the OFCT. From 5 pairs of 76- to 92-year-old Caucasian human eyes and 33 5- to 7-month-old porcine eyes, 5 human and 11 porcine OFCT samples were dissected at the posterior pole or adjacent to the pole in the vertical, horizontal, and radial directions. Sample dimensions were fixed or measured. Tensile tests were performed on the samples in body-temperature saline. The stress-strain relationship was first approximately linear and then became nonlinear. The linear, the neo-Hookean, and the Mooney–Rivlin constants are reported in Tables 1 and 2. No statistical difference was found among their properties in the different directions in either the human or the porcine samples. Statistical differences were found between the human and the porcine material constants in the horizontal and radial directions. Among our material models, only the Mooney–Rivlin model was able to capture the mechanical properties of the OFCT in large deformation properly. The Mooney–Rivlin model was especially adaptive to the human data. This is the first time the mechanical properties of the human and porcine OFCT have been examined in the literature. We believe our data will provide valuable information to others regarding designing implant biomaterials in orbital treatments and developing computer models to study orbital biomechanics.