The creep behavior and solid and melt linear viscoelasticity of novel polyamide 6 (PA6) nanocomposites reinforced with cellulose nanocrystals (CNCs) prepared via in situ anionic ring-opening polymerization (ROP) were investigated to accelerate research efforts to develop new polymeric materials with improved properties for lightweight, load-bearing applications. The obtained results showed that incorporation of relatively small amounts of <= 2wt% CNCs into the PA6 thermoplastic matrix gave nanocomposite samples with significantly enhanced creep and viscoelastic materials functions of the PA6 as indicated by lower creep strain, lower creep compliance, improved elastic recovery after removal of load, and reduced Arrhenius activation energies for time-dependent viscoplastic flow. The obtained results were analyzed and interpreted by theoretical equations for predicting the viscoelasticity and creep behavior of polymeric systems. The melt rheological properties showed enhanced melt strength and elasticity. The formation of a percolated network structure of CNC was revealed by morphological observations that were consistent with the dynamic structure break-up and reformation rheological experiments. The stiffness, rigidity of the CNCs along with their special ROP-facilitated intrinsic strong chemical interactions with the PA6 matrix is believed to be responsible for the observed superior creep and viscoelastic materials functions even with very little CNC concentration. (C) 2016 Society of Plastics Engineers