Abstract: Lipid derivatives represented by the formula: ##STR1## wherein R.sub.1 is alkyl or alkylcarbamoyl; R.sub.2 is lower alkyloxy, lower alkylcarbamoyloxy, lower alkylcarbonylamino, lower alkyloxycarbonylamino, lower alkylureido, lower alkyloxymethyl, lower alkylcarbonylmethyl, cyanomethyl, heterocyclic group, or he0 terocyclyloxy; R.sub.2 ' is hydrogen or R.sub.2 and R.sub.2 ' taken together form --O(CH.sub.2).sub.m -- wherein m is an integer of 1 to 5; R.sub.3, R.sub.4, and R.sub.5 each is hydrogen or lower alkyl or two or three of R.sub.3, R.sub.4, and R.sub.5 taken together with the adjacent nitrogen atom form cyclic ammonio; R.sub.6 is hydrogen or lower alkylcarbonyl; X.sup.- is a counter anion; Y is oxygen or sulfur; and n is an integer of 1 to 10, being useful as PAF antagonists, e.g., as antithrombotic, antivasoconstricting, antibronchoconstricting agent or antitumor agent.