In the United States, an acquittal cannot be appealed by the prosecution because of the constitutional prohibitions against the double jeopardy rule. The US court stated that if the judgment is upon acquittal, the defendant will not seek to have it reversed, and also, the government cannot do it. This was first decided in the case of Fong Foo VS the United States that a judgment of acquittal by a jury cannot be appealed by the prosecution itself. You can click here if you want to learn more about these things in detail.