Blue Mountains National Park was visited by 8.43 million people last year, according to an extensive survey conducted by Roy Morgan Research.
The 2018 park visitor survey, commissioned by the National Parks and Wildlife Service, found that Blue Mountains was the most popular.
It was followed by Royal National Park (6.08m), Ku-ring-gai Chase (3.9m), Kosciuszko (3.27m) and Sydney Harbour National Park (2.42m).
A spokesman for NPWS said 15,645 people were interviewed about their park visitation in the survey. They were randomly selected through both mobile and landline phones.
"Interviews were conducted all year in a series of 13 survey waves, each lasting on average four weeks, to maximise accuracy of recall and help ensure the respondent is actually recounting a visit to an NSW NPWS managed park."
The full survey results can be found at www.environment.nsw.gov.au.