Retailers' sales increased by 0.5 percent in May compared with April, the federal statistics office Destatis said in a statement.
The previous month, retail sales had risen by 1.3 percent.
On a 12-month basis, however, business declined, slipping by 0.4 percent in May compared with the same month last year, the statisticians calculated.
That was because there were two fewer shopping days in May 2015 than in May 2014, Destatis said.
Retail sales data are often revised.