PURPOSE: To obtain a stabilizer for various organic substances, by reacting a phenol with a specified tricyclo[5.2.1.02.6]dec-3-ene.

CONSTITUTION: A phenol is reacted with 1W50mol., per mol. of this phenol, of a lower alkyl-(un)substituted tricyclo[5.2.1.02.6]dec-3-ene of formula I (wherein R1 is a lower alkyl in position 1, 7, 8, 9 or 10, R2 is a lower alkyl in position 2, 3, 4, 5 or 6, and n and m are each 0W5) at -10W200°C for 1W10hr in the presence of a Friedel-Crafts catalyst to obtain a stabilizer comprising a phenolic derivative formed by substituting at least one nuclear hydrogen atom of phenol, an alkylphenol having one or two 1W4C lower alkyl groups in o- and/or p- positions, or bisphenol A with a lower alkyl-(un)substituted tricyclo[5.2.1.02.6] dec-3-yl group of formula II or a lower alkyl-(un)substituted tricyclo[5.2.1.02.6]dec-4-yl group of formula III.