The latest official figures show that the number of new cars licensed in August fell by 64.5% compared with the same month last year.
The Central Statistics Office says that a total of 2,422 new cars were licensed last month, down from the figure of 6,822 in August 2008.
Car sales had fallen by 73% in July.
The figures show that the number of new good vehicles licensed in August came to 869 compared with 1,425 the same time last year - a slowdown of 39%.
Recent figures from the Society of the Irish Motor Industry (SIMI) showed that the first eight months of the year, new cars sales are down almost 64%.
Breaking down today's CSO figures, they show that of the 2,422 new cars sold last month 41.9% were petrol and 56.4% were diesel.
The most popular brand last month was Volkswagen, of which 295 models were sold. Ford was second (291), Toyota third (268), followed by Nissan (223) and Opel (197).
