Uber president Jeff Jones is leaving the company after less than six months.
A source at the taxi booking app told the BBC the resignation was "completely unexpected".
They said Mr Jones was frustrated the company was hiring a new chief operating officer and that he was not among the candidates.
But according to technology news site Recode, Mr Jones left because of Uber's continued struggle with issues around sexism and sexual harassment.
Uber said in a statement: "We want to thank Jeff for his six months at the company and wish him all the best."
Uber has suffered a spate of controversies in 2017, the most serious being ongoing rows over a culture of sexism, and accusations of sexual harassment at the firm.