Documents published by council bosses show the authority is forking out £145,000 each year to keep people out of Hatfield Colliery which closed in 2015.
Around £25,000 of which is used for the site's 'ongoing repairs and maintenance costs' while the final £120,000 is paid to a private security firm - around £2,300 a week.
The cost is not budgeted for and cash is being used from council reserves to pay for it - despite the authority not owning the site.
Latest figures show council reserves stand at £7.8 million.
Council chiefs said the main concern is accidental or deliberate interventions 'by trespassers, opportunist thieves, adrenaline junkies or closure tourists' and the 'reputational damage' it would bring if someone was to get injured on the site.
They added buildings and headstocks pose an 'immediate health and safety risk' as they sit dilapidated and are said to be 'attractive to trespassers who have been known to climb similar structures' creating a 'significant health and safety risk'.
A previous site report back in November reflected that theft and intruder activity had 'been increasing' and security personnel are 'still escorting thieves off site with quads and motorbikes running amok.
In a section of a report compiled by Gillian Fairbrother, assistant director of trading services, she said: "The Hatfield Colliery site is not owned by Doncaster Council. If the council does not take action however, the site will be left without sufficient safety measures in place to prevent access to the remaining buildings and headstocks by the general public.
"The council would be unlikely to be legally liable for any accident which took place on site but would be likely to suffer reputational damage and adverse publicity should there be any. As such, the proposal as outlined is fully supported from an assets perspective."
Scott Fawcus, the council's assistant director of legal and democratic services, said the health and safety position at Hatfield Colliery is 'complex' and has been the subject of 'detailed legal advice'.
"Whilst the Council don’t have legal responsibility for health and safety at the site, as a responsible council, it cannot simply close its eyes and allow a risky site to be open to the public, thus there is a need to continue with the current security arrangements," he said.