The audit by Deloitte was released late Tuesday night after a four-month investigation.
It found more than $131,000 in expenses made by Fennell and her staff went against city rules.
It also said another 79 expenses totalling more than $150,000 may have breached the rules.
Some of the expenses include non-economy flight passes, premium hotel rooms and credit card charges that were not for city business.
The report found no evidence of wrongdoing for a trip to Florida for a sister-city agreement.
It also cleared the mayor of using city staffers for organizing private fundraisers.
Fennell released a statement saying she accepts much of the report but not all of it.
“I have not read all of the report. I accept much of what it has to say, but not all of what it has to say,” Fennell said.
"If there are changes that need to be made, I will make them.”