The invention provides novel .omega.-(5-alkenylthien-2-yl)alkanecarboxylic acids and their functional derivatives having the formula ##STR1## wherein n is an integer from 1 to 9, inclusive; R.sup.1 is H and R.sup.2 is --OH, or R.sup.1 and R.sup.2 together with the wavy lines represent a keto group; and R.sup.3 is H, C.sub.1 -C.sub.6 straight or branched-chain saturated hydrocarbon, or a pharmaceutically acceptable alkali cation. The 3-oxoalkenyl-substituted compounds of formula (I) are prepared by a Wittig-Horner reaction using a 2-oxoheptylphosphonic acid dialkyl ester and an aldehyde of the formula ##STR2## as starting materials, while the 3-hydroxyalkenyl-substituted compounds are obtained by reduction of the corresponding 3-oxoalkenyl compounds. The esters of formula (I) can also be readily converted to the corresponding acids and salts of formula (I).The compounds of the invention have valuable anti-inflammatory, antipyretic and anti-arteriosclerotic properties, yet have low toxicity and do not irritate the gastric mucosa.