They've advised the government to tighten laws around the export of weapons as new figures reveal government licenses and German arms exports had risen 96 per cent in 2015, to £10.9 billion (€13 billion).
Mgr Karl Justen, from the German Catholic Church's Liason Office in Berlin, said: "Over the past 20 years, the federal government's reporting of contracts has become quicker and more transparent, while public awareness and debate around the issue has also intensified.
"But while government policy allows exports to third countries in regions of crisis and conflict only in justified individual cases, the data show otherwise - this is why we're asking for a new law requiring the reasons for arms exports to be stated."
The Joint Conference on Church and Development released a 118-page report on arms exports.
It recommended that Germany should "send a strong signal" by demanding an embargo against Saudi Arabia.
Mgr Justen said it was "completely unacceptable" that £641 million worth of weapons were sold to Saudi Arabia last year, and £1.42 billion to Qatar.
He condemned Qatar for "massively violating human rights and supporting Islamists around the world," and added that both countries had "trampled international humanitarian law underfoot" by engaging in a war which has left 10,000 dead in Yemen.
Germany's arms industry earns £1.62 trillion annually and employs more than 80,000 people. It is the third biggest arms supplier in the world after the US and Russia.