This invention relates to a novel prostacyclin represented by the formula: ##STR1## [wherein R.sup.1 represents --CO.sub.2 R.sup.5 group or --CONR.sup.6 R.sup.7 group; A is(i) --CH.dbd.CH--CH.sub.2 CH.sub.2 -- or(ii) --CH.sub.2 CH.sub.2 --O--CH.sub.2 --;B represents --C.tbd.C-- group; R.sup.2 represents an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, a phenyl group or a phenoxy group;R.sup.3 represents a hydrogen atom, a methyl group or a vinyl group; R.sup.4 represents a hydrogen atom, an acyl group, a tri(1 to 7 carbon atoms)hydrocarbyl-silyl group or a group forming an acetal bond with an oxygen atom of a hydroxy group; a double bond in the substituent represented by A is E or Z, or a mixture thereof; asymmetric center in the substituent represented by R.sup.2 is an R-configuration or S-configuration, or a mixture thereof];and uses in which they are employed as circulation ameliorating pharmaceuticals for blood flow ameliorating, antithrombus and the like, or antiulcer pharmaceuticals.