Police were called to Fairmead Close at 6.40pm after reports of an argument between two men.
A spokesman for Sussex Police said a 61-year-old man, from Fittleworth, suffered a gun shot wound to the leg and was treated by paramedics at the scene.
He was later taken to hospital and his injuries are not believed to be life threatening.
Police said a 70-year-old man was arrested on suspicion of attempted murder. He remains in police custody.
The spokesman said police are not looking for anyone else in connection with the incident and believe there is no further risk to the public.
A police cordon will stay in place at the scene whilst the investigation continues.
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