Eugen von Halácsy (1842 - 1913) was an Austrian physician and botanist of Hungarian descent who was born in Vienna.
In 1865 he obtained his medical doctorate in Vienna, and until 1896 was a general practitioner in Vienna. He is remembered for his three-volume synopsis on Greek flora called Conspectus florae Graecae (1900-08). In 1912 he received an honorary doctorate from the University of Athens. Halácsy's herbarium is preserved at the University of Vienna.