Hi... if I rental a car, will you hold my passport as security?
Never. You will asked to show your passport at the desk so the staff will be able to photocopy it and give back to you straight away.
I have read about some cases in Thailand, where they hold passport as security...
I wouldn't take any notice of what you read on the Internet. It is ILEGAL to hold someone's passport for any reason and you should never allow anyone to do so.