Police were called at 11.21pm to a report of a collision involving a Vespa scooter and Mini Cooper on Copnor Road, close to the junction for Torrington Road.
Sadly, the rider of the scooter, a man in his 30s from Portsmouth, has been pronounced dead.
His next of kin have been informed and are being supported.
Officers are making enquiries as to the exact circumstances of the collision and are keen to hear from anyone who can assist them.
If you witnessed the incident, or have dash cam footage from Copnor Road around 11.21pm or CCTV cameras outside your house which point out towards the road, then we are keen to speak with you.
Anyone with information should call 101, quoting the reference 44200499342.