Retail sales volumes in the 20 nations sharing the euro currency were unchanged from April and were 2.9% lower year-on-year.
That compared with average forecasts in a Reuters poll of economists of a 0.2% monthly rise and a 2.7% decline from a year earlier.
Consumption has been sluggish as real incomes fall and households are now spending a larger part of their incomes on expensive energy and on credit and mortgage repayments, eroding demand for other goods.
Households have also increased their savings because of higher rates and as a precaution at a time of low economic growth.
Retail sales were also flat in April after month-on-month declines in February and March. Year-on-year, retail sales have fallen for eight consecutive months.
Food, drink and tobacco sales fell by 0.5% from April and car fuel sales by 0.3%. Non-food sales were 0.1% higher, although online sales declined by 0.9%. Compared with a year earlier, all sales categories were weaker.