S&P increased the Greek rating from "selective breach of contract", "B minus".
The agency also praised the government continued efforts to cut back on spending.
Greece is now accept the second two rescue.
Last week, the Greek to receive the latest from the European Union and the international monetary fund's rescue funds.
Greece continued to tight work, they agreed to release 49.1 bn euro ($57 billion, 37 billion pounds), and buy some debts.
Bn 240 euro, altogether has been reserved the Greek rescue loans.
So far, Greece has received nearly 149 bn euros (?119 bn $191 bn) from the euro zone and the international monetary fund (IMF), the bn 240 euro.
S&P said in a statement: "upgrade reflects our European economic and monetary union (eurozone) members of the strong determination to keep Greece in the eurozone members.
"Long-term rating prospect is stable, balanced fiscal and structure adjustment of economic and political challenges, so that we think the government commitment."
The Greek for help, in order to meet its debt payments, after many years of overruns means it can't keep up with their debts.
Negative market think the Greek worse, because it is pushing up the rate of return or interest level of country must provide the new government bond sales, to attract buyers.
The British broadcasting corporation economic editing Stephanie Flanders S & P said in a notice: "this is a major upgrade, the government will consider dropping confidence vote, but it seems to be a general ticket in the euro zone's confidence.
"Greece is not economic woods, any imagination, but financial markets now think of Greece in the euro area from less likely.
"S&P to catch up with the upgrade and market optimism. Theoretically, a large part of the Greek sovereign debt restructuring, has also made a breach in the future is unlikely.




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