The banks, in which the Russian state holds a majority stake, include the country's largest lender, Sberbank. The others are Gazprombank, Rosselkhozbank, VEB and VTB bank.
The latest sanctions were announced on Tuesday but the names of the targeted firms and other details were only released today.
The package of punitive measures also includes an arms embargo and the prohibition to export some oil exploration technology used for deep water drilling, Arctic oil exploration and production, or shale oil projects.
The EU is Russia's biggest trading partner. The sanctions with the most immediate effect are those targeting the banks because they make access to finance for Russia's already ailing economy harder and further spook international investors who fear running afoul of the sanctions regime.
The EU beefed up its sanctions against Russia over what it decries as Moscow's meddling in Ukraine after the downing of a Malaysia Airline passenger jet earlier this month over eastern Ukraine, which killed all 298 people aboard. The U.S. and Ukraine say the Boeing 777 was shot down by a missile fired from areas controlled by pro-Russian separatists. The regulation laying out the new sanctions, which will take effect Friday, said it will be prohibited for EU firms or citizens to "directly or indirectly purchase, sell, provide brokering or assistance in the issuance" of debt instruments by the Russian banks targeted.