Auditor Gordon Sutton, in his annual management letter, said there was 'a culture that has grown that needs to be looked at.'
The culture in question includes frequent trips by councillors to exotic locations on club and business class flights and the operation of a free lunch and bar on race days at the council-owned Doncaster race course.
Some of the foreign trips to overseas racecourses by councillors were recorded as being undertaken to develop expertise in the running of the course.
Of particular concern is the relationship with Doncaster 2000, a partnership between the council and local building and development firm Keepmoat. The auditor believes an agreement between the two by which Keepmoat gets first refusal on all surplus council land is possibly illegal. The next report is expected in two to three weeks time.
In his report the auditor said: 'I would ask members to ensure that action is taken as a matter of urgency.
'There are serious concerns over the lack of control in some sensitive areas.'
He said rules on expenses claims were unclear, which had led to inconsistencies and abuse.
A spokesman for Doncaster said new draft guidelines had been produced in response to the report and the amount concerned was a tiny proportion of the council's spending.
'It is less than one-tenth of 1% of the overall budget. Nevertheless as a prudent authority we take this very seriously.'