To provide a method for producing a norbornene-based polymer in a high polymerization activity by using a metallocene-based catalyst.

This method for producing a norbornene-based polymer by polymerizing monomers at least containing norbornenes and producing the norbornene-based polymer containing at least ≥0.1 wt.% recurring unit originated from the norbornenes, is provided by using the norbornene obtained by making the 1 L of norbornene in contact with 100-2,000 g alumina or the 1 L of the norbornene in contact with 0.001-100 L of ≥0.01 N alkaline water.