PURPOSE: To provide the titled stable composition having contracting and dilating activities to the arterial wall, and useful as a precursor of a preventive for thrombosis, arteriosclerosis, etc., by compounding a specific compound such as phosphatidylethanolamine, etc. as a stabilizing agent.

CONSTITUTION: At least one compound selected from the compounds of formula I (R1 and R2 are fatty acid residue) is compounded as a stabilizer of an eicosapolyenoic acid compound. There is no particular restriction in the amount of the stabilizer, however, the especially preferable amount is ≥10wt% based on the eicosapolyenoic acid compound. The stabilizer may be further incorporated with an arbitrary amount of the compound of formula II (preferably phosphatidylcholine). An especially preferable example of the compound of formula I is phosphatidylethanolamine.