urrent finite element models of the human lower extremity lack the accurate constitutive representations of knee ligaments necessary for computational evaluation of pedestrian injury countermeasures. The collateral ligaments have been reported to be the most frequently injured knee ligaments in pedestrians involved in automobile collisions. The purpose of this study is to determine the material and failure properties of human collateral knee ligaments tested in tension to failure at two different rates. Four lateral collateral ligament (LCL) specimens and 4 medial collateral ligament (MCL) specimens are tested to failure in tension at a high rate (1600 mm/s), and 4 LCL and 4 MCL specimens are tested to failure at a low rate (1.6 mm/s). Each specimen consists of a bone-ligamentbone complex and the tensile direction is representative of joint distraction at 0° flexion. 3dimensional non-contact surface digitization is used to calculate the cross sectional area of each ligament. The Lagrangian strain of the surface of the ligament is calculated by speckle pattern motion recognition. The average LCL ultimate stress and elastic modulus (39.3 MPa and 477.9 MPa, respectively) are more than double the ultimate stress and elastic modulus of the MCL (15.98 and 138.3, respectively). The data show that in both ligament types, the stress at a particular strain in an average high rate test is significantly greater than the stress at the same strain in an average low rate test (p<0.001), proving the presence of rate sensitivity over the range of strain-rates examined (1%/s-2400%/s).