To use a decomposition catalyst polymer of a triazine compd., such as triazine type agricultural chemicals or insecticides, containing a triazine compd. as a matrix in the detoxification of a triazine compd. harmful in environment.

A decomposition catalyst polymer of a triazine compd. is synthesized by a matrix polymn. method using a triazine compd. represented by the formula (wherein X is a halogen atom, a 1-5C alkylthio group, a mono 1-5C alkylamino group or an amino group and R1 and R2 are each independently a 1-5C alkyl group) as a matrix in the coexistence of a prepolymer having a proton free group.