'New realities'
He said the 2016 budget should be revised to assume an oil price of $40 a barrel.
"Our task is to adapt our budget to the new realities," Mr Siluanov said. Image copyright Image caption Economy Minister Alexei Ulyukayev warned that Russia faced a long period of low commodity prices with oil at $15 or $20 a barrel.
"The biggest risk is that there will be low prices for a long time - that is, for years, for decades," he said.
Mr Medvedev also said that high interests rates were holding back economic growth in Russia.
The Bank of Russia held rates at 11% last month, with governor Elvira Nabiullina warning of "high volatility" in global markets.
A year ago the central bank shocked markets by increasing rates from 10.5% to 17%.
Inflation stands at 15% in Russia, but the bank hopes it would fall to 4% by next year.