Tendon which is a specialized connective tissus made of collagen with complex three dimensional structure with viscoelastic behavior shows variable biomechanical changes with species, age, activity levels, testing environments, testing rate, gripping technique, storage methods etc... Fifty long flexor digitorum profundus tendons of Habbard chickens, 40-days-old and weighing 1.65 Kg. on average, with Instron 1000 testing machine at vsrious tension speed of 0.5mm/min(Group I, l. 25% stain/min), 1mm/min(Group II, 2.5% strain/min), 10mm/min (Group III, 25% strain/min), 100mm/min (Group IV, 250 % strain/min, and 250mm/min Group V, 625% strain/min) to determine the biomechanical changes at various increment of tension speed. Mechanical parameters such as yielding strain, maximum strain, yielding load, maximum load, yielding stress, maximum stress, modulus of elasticity, total energy absorption density (modulus of toughness) were analyzed. Yielding load, maximum load, yielding stress, maximum stress, modulus of elasticity, modulus of toughness significantly increased at higher tension speed (p<0.01). Strain at yielding point and maximum load did not increase significantly with increment of tension speed (p<0.05). The increase of the aforementioned parameters showed the trend of reaching a plateau at certain higher strain rate between 2.5% strain/min and 25% strain/min.