Police responded to reports of a fight in Hawkswood Road, Hailsham at 6.20pm on Monday, August 30.
Officers attended and secured the area outside a parade of shops, and paramedics were also called.
One teenager was taken to hospital with his injuries. He is now in a stable condition.
A second teenager suffered a minor injury and also attended hospital but he has since been discharged.
Officers at the scene arrested a teenage boy on suspicion of inflicting grievous bodily harm, he remains in custody at this stage.
Witnesses or anyone with information about the incident is asked to report it to Sussex Police online or call 101 and quote Operation Spray.
Officers will be carrying out patrols and speaking with residents in the community to provide reassurance while the investigation continues.