The incident happened on Tuesday (August 31) at 7.10am on Station Road in East Preston, when the rider collided into street furniture, police said.
Sussex Police have identified the rider as a 15-year-old boy and have informed his next of kin.
Detective sergeant Rob Baldwin of the serious collision investigation unit, said: “This is a tragic incident involving a child and we are conducting a thorough investigation to establish the circumstances.
“I would appeal to anyone with information, who has not yet been spoken to by police, to contact us as soon as possible.
“We are particularly interested in dash camera footage or CCTV showing a green and silver motor scooter being ridden around the local area prior to the collision.”
Anyone with information is asked to call 101 or email [email protected], quoting Operation Hawthorns.