Police were called to reports of a serious assault at Sandford Holiday Park near Wareham in the early hours.
The man was pronounced dead at the scene and a 41-year-old was arrested on suspicion of murder.
The arrested man - from Torquay - is believed to be known to the victim, who has not yet been formally identified.
Det Insp Mark Samuel said: "Following the discovery of a man's body, inquiries are now under way to establish exactly what happened during the early hours of this morning.
"I understand that the holiday park was busy at the time of the incident and I would urge any witnesses, who have yet to speak with the police, to contact us as soon as possible."
A murder inquiry has been launched after a man died at a Dorset holiday park.