Some new oximinoalkanoic (n = 2,3,4) esters and acids derived from methoxyphenylthienyl ketones have been synthesized and evaluated in vitro for their inhibitory effects on arachidonic acid-induced human platelet aggregation. Of the eighteen oximinoethers tested the most active derivatives, which were four times more active as aspirin, belonged to the para methoxy series with Z configuration and n = 2 or 3.