Racing Victoria (RV) said its chairman David Moodie had stood aside pending an investigation by Racing Integrity Commissioner Sal Perna.
The governing body said in a statement that the probe related to "a matter" that had been reported to Perna by the body's independent Integrity Council but provided no further details.
Local media reported Moodie was being investigated over allegations of impropriety relating to inappropriate disclosures of information.
Moodie took over as chairman in May last year after predecessor Robert Roulston's sudden resignation in the wake of an internal audit.
Moodie could not be reached for comment by Reuters.
Australian horse racing has been blighted by a string of doping and corruption crises that have tarnished the image of the multi-billion dollar industry in recent years.
Several leading trainers were handed lengthy suspensions last year after their horses failed drug tests for cobalt, a naturally occurring element in horses that can be performance-enhancing at elevated levels.
The Melbourne Cup, the world's richest two-mile handicap, has not been immune to the scandals, with controversial local jockey Damien Oliver permitted to ride in the 2012 race on Americain despite a media storm over his complicity in an illegal betting scandal.
The 156th running of the Melbourne Cup is on Nov. 1.
(Reporting by Ian Ransom; Editing by Amlan Chakraborty)
