Mark Hurd + resigned effective immediately
Mr Hurd stepped down from his positions as president and CEO after an investigation into claims made against him by a former HP contractor.
The company said its sexual harassment policy had not been violated but its standards of business conduct were.
HP has named chief financial officer Cathie Lesjak as its interim CEO.
'Painful decision'
The company said: "Chief executive officer and president Mark Hurd has decided with the board of directors to resign his positions effective immediately."
In a statement, Mr Hurd said he "realised there were instances in which I did not live up to the standards and principles of trust, respect and integrity that I have espoused at HP".
He said: "This is a painful decision for me to make after five years at HP, but I believe it would be difficult for me to continue as an effective leader at HP and I believe this is the only decision the board and I could make at this time."
Ms Lesjak, who has been at HP for 24 years, will continue to act as chief financial officer while the company's board committee searches for a new CEO.
The departure of Mr Hurd is likely to come as a shock to investors, who have credited him with reviving HP's fortunes since taking over as boss five years ago.
His strategy of drastically cutting costs, and thousands of jobs, allowed HP to overtake Dell as the biggest manufacturer of PCs in the world in 2006.
On Friday HP issued preliminary results for the third quarter slightly above expectations.
Source:bbc