Thermoplastic polyurethane (TPU) composites containing carbon nanotube (CNT) with the loading ratios from 0.5wt% to 2 wt% were prepared using melt-compounding process. Surfaces of the CNT particles were treated with sulfuric acid/nitric acid to purify CNT and to achieve compatible surface characteristics between TPU matrix and CNT. Mechanical, thermal, flame retardant, melt flow, and morphological properties of TPU/CNT composites were investigated. Addition of CNT to TPU matrix causes in a prominent increase in tensile strength, percentage of elongation at break, and tensile modulus values of TPU. The mechanical properties are improved for lower modified CNT loadings. CNT inclusions also improve the thermal stability of pristine TPU. Addition of CNT into TPU matrix causes increase in melting and decomposition temperatures of TPU and decrease in glass transition temperature. The flammability parameters of TPU also shift to higher values after CNT loadings to matrix. Modified CNT additions at higher concentrations exhibit better fire performance. Additions of modified CNT and pristine CNT show different trends in the case of melt flow rate values. Modified CNTs disperse more homogeneously relative to pristine ones into TPU matrix which is due to improvement in interfacial interactions between CNT and TPU.