The investigation, which involved an employee who was not under his direct supervision, determined that Huston had engaged in activities inconsistent with the board's expectations for executive conduct, Priceline said.

The travel website operator said Huston, who has been the company's CEO since January 2014, had acknowledged his misconduct and expressed regret.

"This did not involve issues about the company's financial statements, accounting or internal controls over financial reporting," Leslie Cafferty, a company spokeswoman, told Reuters in an email.

Huston will not receive any severance payments, the company said in a regulatory filing.

"I am satisfied with the Board's thorough review of this issue," James Guyette, lead independent director who is also overseeing the CEO search, said in a statement.

Chairman and former CEO Jeffery Boyd replaces Huston on an interim basis.

Huston will also step down as CEO of Booking.com, a unit of Priceline. He will be replaced by Booking.com Chief Operating Officer Gillian Tans.

Huston's resignation comes just days before the company is scheduled to report its second-quarter results on May 4.

Shares of the company were trading down 1.2 percent at $1,338 in premarket trading. They have gained 6.2 percent in value this year.