This study examined the time-dependent response of bovine periodontal ligament (PDL). Applying linear viscoelastic theory, the objective was 1) to examine the linearity of the PDL's response in terms of its scaling- and superposition property and 2) to generate the phase-lag vs. frequency spectrum graph. PDL specimens were tested under three separate straining conditions: 1) tension ramp tests conducted at different strain rates, 2) pulling step-straining to 0.3 in discrete tests and to 0.3 and 0.6 in one continuous run, 3) Tension-compression sinusoidal oscillations. To this effect, bar-shaped specimens of bovine roots that comprised portions of dentin, PDL tissue and alveolar bone were produced and strained in a microtensile machine. The experimental data demonstrated that neither the scaling nor the superposition properties were verified and that the viscoelastic response of the PDL was non-linear. The PDL's elastic response was essentially stiffening and its viscous component was pseudo-plastic. The tangent of the PDL's strain-stress phase lag was in the 0 - 0.1 range in the tensile- and in the 0.35 - 0.45 range in the compressive directions. In line with other biological tissues, the phase lag largely independent of frequency. Using the data generated, a mathematical model is outlined that reproduces both the elastic stiffening and viscous thinning of the PDL's response.