The invention relates to new optically active or racemic 13-thia-prostacycline derivatives of the Formula I ##STR1## wherein R.sup.1 is hydrogen, a pharmaceutically acceptable cation or a straight or branched chain alkyl group having 1-5 carbon atoms;R.sup.2 is straight or branched chain alkyl having 4-9 carbon atoms or monosubstituted phenoxymethyl;--A--B-- is --CH.sub.2 --CH.sub.2 --, --CH.dbd.CH-- of Z-- or E-- configuration or --C.tbd.C--;one of the symbols X and Y is hydrogen, methyl or ethyl and the other is hydroxy, tetrahydropyranyoxy, 1-ethoxy-ethoxy or trialkylsilyloxy; orX and Y together form a --O--CH.sub.2 --CH.sub.2 --O-- group;Z is a sulfur atom or a --SO-- group.The compounds of the Formula I can be prepared by reacting a 13-thia-prostaglandine of the Formula III ##STR2## if desired after oxidation into the corresponding 13-oxide derivative--with a halogenating agent; and treating the 5-halogeno-13-thia-prostacycline of the Formula II ##STR3## thus obtained wherein E is halogen with an organic or inorganic base; and thereafter if desired removing the protecting groups X and/or Y and if desired converting a compound of the Formula I obtained into a salt or setting free the same from a salt. The new compounds of the Formula I possess anti-coagulant and hypotensive properties and can be used in therapy.