Considering the long-term structural stability of polymer-nanotube composites under different service conditions, we investigate the tensile creep of polymer-nanotube composites consisting of poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotubes (MWCNTs). The PMMA is pre-irradiated by ultraviolet light with different doses to change the molecular weight. The creep deformation of the PMMA-MWCNT composites with the weight fraction of MWCNTs in a range of 0 to 0.7 wt.% in a temperature range of 50 to 80 °C is well described by a Maxwell standard model with parallel connection between a spring, E1, and a Maxwell element (a dashpot, η, in the series connection with a spring, E2). The value of E1 is a linear function of the inverse of the normalized weight fraction with the average values of the coefficients/constants for the linear relation being increasing functions of the weight fraction of MWCNTs. The value of η is a power function of the molecular weight with a power index of ~3.3. The activation energy for the creep deformation of the PMMA-MWCNT composites increases with the increase of the weight fraction of MWCNTs.