The UN's Monusco mission said the peacekeepers were attacked by suspected rebels of the Allied Democratic Forces (ADF) in North Kivu province, BBC reports.
Five soldiers with the DR Congo's armed forces (FARDC) were also killed.
UN Secretary-General Antonio Guterres described it as the worst attack on UN peacekeepers in recent history.
He sent his condolences to Tanzania, their home country.
Read alsoPoroshenko says Ukraine united EU around idea of peacekeeping mission in DonbasEastern DR Congo has suffered years of instability with rival groups fighting for control of territory.
A Monusco statement said rebels had launched an attack against an operating base at Semuliki in Beni territory on Thursday evening.
"This resulted in protracted fighting between suspected ADF elements and Monusco and FARDC Forces," it added.