The rating agency confirmed that Greece's short-term credit rating was raised to B and the long- term to B-, based on the government's commitment to fiscal and structural adjustment on the way to recovery, reported Xinhua.
The upgrade "reflects our view of the strong determination of European Economic and Monetary Union member states to preserve Greek membership in the euro zone", Standard & Poor's said in a statement, justifying the decision.
This move came after recent positive developments regarding the Greek debt crisis, such as Euro Group's approval for the release of the next bailout aid and the successful debt buyback plan.
Financial analysts in Athens noted that the upgrade was expected as normal procedure, but they welcomed its quite "generous" extent by six notches, as financial news daily "Naftemporiki" (Shipping News) commented.
Standard and Poor's had cut Greece's rating to selective default Dec 5 ahead of the Greek bond buyback program which further eased the country's debt load by some 20 billion euros ($26.4 billion).
Greece's credit rating has been repeatedly downgraded by international agencies over the past three years, since the start of the acute Greek debt crisis.