The 78-year-old was riding on the B800 Kirkliston-South Queensferry road near Edinburgh, police said.
A black Mercedes B class car struck the silver mountain bike about at about 10am.
Road policing sergeant Ross Drummond said: "I am appealing for anyone who saw either the man on his bike - he was wearing every day clothing and was not in specialised cycling clothes - or the car around this time. We would like to hear from anyone who can assist us in any way."
The driver of the car, who was uninjured, stopped and has been helping police with the investigation.