Sales of food, drinks and tobacco decreased 3.3% on the month in August in data adjusted for the number of working days and seasonal factors, while non-food sales were down 2.5%.
However, fuel sales inched up 0.6% in August from the previous month, INS said.
In annual terms, adjusted retail sales declined 5.9% in August, largely due to a 10.5% decrease in food sales.
Sales of non-food items fell 2.1% on the year in August, but fuel sales increased 0.4%.
In January through August, Romanian adjusted retail sales declined 5.3% on the year, due to falling consumption in all sectors, the data showed.