Different mixtures of thermoplastic polyurethane (PU) with different amounts of nanometric carbon black (CB) were prepared by mechanical stirring in organic solvent, and their thermal, rheological, viscoelastic and mechanical properties were investigated. The rheology of the PU-CB mixtures in methyl ethyl ketone was optimized, allowing good dispersion of the CB in the polyurethane matrix once the solvent was removed; an increase in the number and size of carbon black aggregates in the polyurethane matrix was obtained by increasing the carbon black loading. Addition of carbon black improved the rheological and viscoelastic properties of the polyurethane, and the larger was the carbon black content, the higher was the storage modulus and the lower was the tan delta value. Moreover, the addition of higher amounts of CB changed the viscoelastic behaviour of the polyurethane, which became mainly elastic over all temperature range. On the other hand, the addition of CB loadings up to 12wt% increased the thermal stability of the polyurethanes and increased the elongation-at-break without noticeable reduction in the tensile strength.