Ambulance crews were called at 18:30 GMT to Ancaster Road after reports that a man had been wounded. He was taken to hospital but later died.
Two men were seen running from the scene, Suffolk Police said. The force is appealing for witnesses.
The road is closed between the junction with Ranelagh Road and Gippeswyk Avenue while officers investigate.
Det Ch Supt Simon Parkes said: "At this early stage of the investigation any piece of information - however small it may seem - could be crucial in helping us to locate the person or persons responsible."
A murder inquiry has been launched after a man was stabbed to death in Ipswich.