Rat tail tendon (RTT) collagen has been crosslinked with 1% basic chromium sulfate (BCS) at pH 3.2, and 2, 4, 8, and 10% formaldehyde (HCHO) at pH 5 and pH 8. The viscoelastic behavior (such as stress relaxation behavior for BCS and HCHO-tanned RTT) has been studied in water and 6M urea at different temperatures. The total rate of relaxation has been divided into fast and slow components, and computed using the two-term model and nonlinear least-squares fit. The rate of relaxation for crosslinked RTT is less than the native one. Activation energy at absolute zero has been computed using k = AT(m)e(-E0/RT) and nonlinear least-squares fit. The activation energy increases for crosslinked RTT than the native one. This is consistent with the observed rate constant values. This may be due to the additional stability imparted to RTT collagen by coordinate covalent and covalent crosslinks through BCS and HCHO, respectively.