It's expected to be thinner and lighter than the wildly popular iPhone 4, but it isn't expected to look that much different from the iPhone 4.
The biggest difference is Apple's latest iOS mobile software, which will include an 8-megapixel camera, email and web browsing apps, plus a new feature, called iMessage, will allow phone users to send text messages to each other over Wi-Fi networks.
The new iPhone is also expected to include Apple's new iCloud service, which will store content, including music, documents and photos on Apple's servers.
It's been more than a year since the company unveiled the iPhone 4.
Tuesday's event will be Apple's first major product unveiling in years that won't be led by Steve Jobs, who resigned from the CEO post in August after being out on indefinite medical leave since January.
His successor, Tim Cook, is expected to take the lead this time.
Analysts believe Apple could also use the event to trot out new iPods and updates to its iTunes music software, which it usually does in the fall anyway.
The Associated Press contributed to this report.