The Mountain View, Calif.-based company said its new version is faster and won't crash even if a user loses connection with a wireless network.
Users can open recently read messages and compose emails even when the phone is offline.
The application is also more similar to Gmail on a computer and includes search, threaded conversations and a new "floaty bar" for more convenient functionality.
The floaty bar appears near the top of the screen with options such as archive, delete and view more options -- and stays with there even as users scroll through their inbox.
"We wanted to make sure that if you are an iPhone user, you can always have a Gmail-like experience on your device," said Shyam Sheth, a product manager for Google Mobile.
The iPhone comes integrated with Gmail, but Apple controls that software code, so Google wasn't able to tweak it and improve the experience.
The new Gmail is compatible with any browser that conforms to the new HTML5 and Gears programming standard.
