Local media reported that the pair were moving through thick bushes near the town of Postiglione, in the province of Salerno, when the incident occurred.
The 34-year-old opened fire when he saw a shadow and rustling leaves.
He immediately raised the alarm when he realised what had happened.
Doctors could do nothing to save 55-year-old Martino Gaudioso.
Both men were in a national park area where hunting is prohibited, reports said.
Police have seized their rifles.
Similar hunting incidents have recently occurred in Italy.
Last October, an 18-year-old was shot and killed close to the French border.
By the end of that month, two more men – a 56-year-old and a 20-year-old – had also died in similar circumstances.