He has sent a memo to staff in his division stating that he intends to "take a long break", citing tiredness as a reason for his departure.
Insiders told the Financial Times that Mr Cai has been considering setting up his own private equity fund in the last few months.
An internal memo has confirmed that David Chin, co-head of Asia investment banking, is to take over Mr Cai's role at UBS' operations in the region on an acting basis.
"UBS is not dependent on a single rainmaker in China and has dozens of capable bankers who can continue Henry's work," a source said.
In May, UBS reported pre-tax revenues of 2.8 billion Swiss francs ($2.57 billion) across its operations in the first quarter of the year, with all of its business divisions recording a profit.
By Gary Cooper