Abstract: Provided are a thiol-reactive polyoxyalkylene-modified lipid which can be used to chemically modify bioactive substances and which can be used for drug delivery systems such as liposomes and a method for producing the same. The polyoxyalkylene-modified lipid is represented by the following formula (1): (wherein, R1 and R2 are hydrocarbon groups which are the same as or different from each other and which contain 4 to 24 carbon atoms, R3 is a divalent hydrocarbon group containing 1 to 6 carbon atoms, OA is oxyalkylene groups containing 2 to 4 carbon atoms, n is the average addition mole number of the oxyalkylene groups and is 5 to 1,000, and Z is a group containing either maleimide or iodoacetamide.