Prince Charles is a strong environmental supporter
He says the attraction would destroy the city's character, according to a trust of which he is the patron.
The prince is in Romania for a four-day private visit organised by the Mihai Eminescu Trust, a British group which supports the preservation of the Romanian countryside.
The Dracula park is to be built in Sighisoara, the home town of 15th century prince Vlad the Impaler - the model for Bram Stoker's fictional anti-hero Count Dracula.
Vlad Tepes was born in Sighisoara in 1431, and gained his bloodthirsty reputation from his habit of impaling Turkish prisoners alive on wooden stakes.
The Romanian Government hopes the park, expected to be finished in 2003, will attract one million visitors a year.
But Greenpeace has argued the project threatens nearby ancient forests and a UNESCO-protected medieval citadel.
'Tragic loss'
In a statement, the trust said Prince Charles thought that "the proposed Dracula park is wholly out of sympathy with the area and will ultimately destroy its character".
Such a project would "be a tragic loss for the local inhabitants and for Europe as a whole", the statement said.
The Prince of Wales is a strong supporter of environmental issues and has travelled through north-west Transylvania, revisiting a group of villages he hopes to restore and regenerate.
He has been interested in the Romanian countryside since the 1980s, when under the rule of Communist dictator Nicolae Ceausecu's, Romanian villages were destroyed to move farmers to apartment buildings in cities.
On Monday, Prince Charles visited the 15th century Bontida castle in avillage near the city of Cluj, about 260 miles north-west of Bucharest.
Several British organisations, including the Prince of Wales Foundation, have been paying for the castle's restoration.