The memo gave no reason for his resignation. The Wall Street Journal, which first reported Fang's departure, said he had emerged as a key figure for U.S. authorities as they investigate whether the investment bank violated bribery laws by improperly hiring the relatives of well-connected Chinese officials.
Fang, 48, could not be reached for comment. A spokesman for JPMorgan declined to comment.
A source familiar with the matter said Fang would leave with immediate effect.
Frank Gong, will be promoted to chairman of investment banking for China from vice chairman, according to the memo obtained by Reuters on Monday. Brian Gu and Jing Zhao will become co-heads of investment banking for China with Jing also continuing in her current role as head of the Financial Institutions Group for Emerging Asia.
U.S. authorities are examining whether JPMorgan's hiring of China Everbright Group Chairman Tang Shuangning's son helped the bank win assignments from Everbright, the Journal said, adding that JPMorgan has provided U.S. prosecutors with emails from Fang discussing the hire.
JPMorgan has withdrawn from underwriting a $3 billion Hong Kong listing by China Everbright Bank Co Ltd - one of two China initial public offerings it has stopped working on while the investigation is being carried out.
Representatives for JPMorgan and China Everbright did not respond to requests for comment on the hiring of Tang's son.
Fang has strong ties to the Chinese government, having been appointed to the Chinese People's Political Consultative Conference in March 2008 for a five year term.
Other firms that have come under scrutiny for their hiring practices in Asia include Citigroup, Goldman Sachs and Morgan Stanley.
UBS AG has placed two Hong Kong-based bankers on leave of absence as part of an investigation over the hiring of an employee related to a Chinese corporate client, IFR reported last month.