The effect of average molecular weight (Mw) of polyoxymethylene (POM) on melt viscosity and solid state creep compliance were investigated. Viscosity follows the power function of Mw. Creep compliance results indicate that time-temperature superposition applies to POM copolymers. Creep compliance in ashort time (0.25 s) is independent of Mw, but in a longer time (10 years) it follows an inverse power law relation with Mw, up to a critical value of Mw = 81 100, where creep compliance becomes independent of Mw. At intermediate time (17 min), similar to short one, no effect on susceptibility to creep compliance was observed. It was also stated that the activation energy is independent of Mw.