Recycled polyethylene terephthalate (rPET) nanocomposites with various amounts of montmorillonite clay (MMT) have been manufactured by using twin screw extrusion. By rising MMT weight content Wf up to 1 wt.% it is possible to increase yield strength and ultimate strength of the composite by 17% and 27% respectively in comparison to neat rPET. Introduction of MMT in the rPET leads also to considerable increase of the modulus of elasticity E. Relationship E(Wf), however, is non-linear and is characterized by slow-down in E growth along with increasing MMT content. At low nanofiller content experimental results are sufficiently well described by using the method of Mori–Tanaka and the solution of Eshleby for the case of completely exfoliated chaotically oriented nanoparticles of MMT. Results of the investigation of long-term creep with duration of 5000 h testify that introduction of MMT in the rPET matrix leads to reduced creep of the composites. Equation of power law can be used for sufficiently reliable prediction of long-term creep of the investigated materials by the method of extrapolation to the time period, exceeding length of the short-term experiment by 50 times.