Olympus, which is recovering from a huge accounting scandal, said in a joint statement with Sony on Friday that the deal first announced in September was held up over approvals from an unspecified authority.
"The examination by the relevant authority is taking longer than expected, but we understand the examination process is currently in its final stage," it said.
Both firms declined to elaborate on specifics of the delay.
But sources confirmed to AFP that the hold up was linked to Chinese regulators. The issue comes at a time when Tokyo and Beijing are embroiled in a tense territorial spat over an island chain in the East China Sea.
Regulatory delays involving other Japanese firms have been linked to hold ups from Chinese watchdogs.
Among them are advertising firm Dentsu's now-completed $4.8 billion takeover of Britain's Aegis and a merger between steelmaker JFE Holdings and Japanese heavy machinery firm IHI.
The problem comes as regulatory delays involving Japanese advertising firm Dentsu's now-completed $4.8 billion takeover of Britain's Aegis media group have been linked to hold ups from Chinese watchdogs.
Sony and Olympus had initially planned the launch of a joint venture from April 1 as Sony, which is trying to repair a dented balance sheet, invests 50 billion yen ($532 million) in Olympus as part of a drive to tap the lucrative medical equipment market.
Better known for its cameras, Olympus controls about 70 percent of the global market for medical endoscopes.