Chancellor Angela Merkel may run the country but women only make up 2.5 percent of the members of executive boards at the 200 biggest German companies, holding 21 seats out of 833, according to the study by the German Institute for Economic Research (DIW) in Berlin.
Among the 30 firms listed on the DAX blue-chip index, electronics giant Siemens is the only group to have a woman on its board, it said.
The situation is slightly better on German corporate supervisory boards, with 10 percent of seats held by women. But most represent employees rather than management.
"There will be no change in this trend without binding rules," the study concluded, citing the example of Norway, which mandates that companies must reserve 40 percent of seats on executive boards for women.
In France, parliament last month adopted a similar draft bill requiring the 650 listed companies to offer 40 percent of seats on their executive boards to women within six year of the law's passage.
Merkel was elected Germany's first female chancellor in 2005. Forbes magazine has named her the world's most powerful woman four years running.