A sphingomyelin analog represented by the following formula ##STR00001##
wherein R.sup.1 is C.sub.1-20 alkyl group, R.sup.2 is C.sub.1-20 alkyl
group, aryl group or C.sub.1-6 alkyl group substituted by aryl group, and
Z is photoaffinity-labeled group, or its optically active compound.