Clay is a soil component, a ceramic ware component, and a reinforcement in nanocomposites. Its viscoelastic behavior is relevant to vibration damping and slip rheology. The clay studied is hectorite, which is a trioctahedral magnesium-based smectite. Clay compacts with solid contents (50-53) vol% are studied in terms of the dynamic compressive properties at small static strains (3.1-3.5 %), low deformation amplitudes (5-8 mu m), and low frequencies (0.2-10.0 Hz). The organic intercalation of hectorite (with basal spacing 12 prior to intercalation) to form organoclay (nanoclay in the form of disteardimonium hectorite with basal spacing 29 ) increases both the loss tangent and the loss modulus of the solid part of the compact by up to about 27 %, while affecting the storage modulus negligibly. At 10.0 Hz, the organic intercalation increases the loss tangent of the solid part from 0.306 +/- A 0.009 to 0.366 +/- A 0.021 and increases the loss modulus of the solid part from (2.69 +/- A 0.08) x 10(4) to (3.44 +/- A 0.04) x 10(4) Pa. The organic intercalation affects the viscous behavior rather than the elastic behavior. The viscous behavior is attributed to the low-amplitude dynamic slippage at the interface between adjacent clay layers in a clay nanoplatelet and that between nanoplatelets in a clay particle. In case of organoclay, it is also due to the nanoscale viscous behavior of the organic component. The viscoelastic properties are essentially independent of the frequency. The viscous character of both unmodified clay and organoclay is weaker than that of carbon black or exfoliated graphite, but the elastic character of both unmodified clay and organoclay is stronger than that of carbon black or exfoliated graphite.