The elongational viscosity of HDPE and the same polymer filled with glass beads was measured. The strain-hardening of neat HDPE showed anomalous strain rate dependence; the behaviour became weaker as the strain rate increased. The strain-hardening of the HDPE filled with glass beads weakened with increasing bead contents. Suppression of the strain-hardening by the beads is stronger at high strain rate, where the strain-hardening of neat HDPE is weak. Especially, the strain-hardening did not appear if the bead contents and the strain rate are sufficiently high.