The stabbing took place in Elphick road, Newhaven around eleven thirty in the evening on Monday 6th January and a sixteen year old has been arrested on suspicion of murder.
Armed officers attended the scene as well as the air ambulance.
Despite every effort being made the man was pronounced dead at the scene.
The victim is thought to be an eighteen year old and it is believed that the victim and assailant knew each other.
The area has been cordoned off while forensic teams and police carry out their investigations.
Police would be interested to hear from any one who may have been in the area and may have witnessed the incident.