The CSO says a total of 10,469 new cars were licensed last month, down 527 from the 10,996 licensed the same time last year.
Read the full CSO report
The CSO says that out of the 10,469 new cars sold last month, 35.2% were petrol and 60.6% were diesel.
The most popular brand of new car sold last month was Ford, followed by Toyota, Renault and Volkswagen.
Today's figures are in marked contrast to figures from the Society of the Irish Motor Industry released earlier this month.
The SIMI figures showed a 5% increase in January sales and said the increase was due to buyers' interest in the Government's scrappage scheme.
The SIMI figures for new cars are based on registrations, while the CSO numbers are based on when the car is taxed.
The SIMI said that due to bad weather in early January, most registrations took place late in the month and due to a gap between registration and taxation this could have affected the figures.
It says it is still expecting new car sales of around 70,000 this year, up from 54,400 last year, helped by the scrappage scheme.
