The 52-year-old woman had been cycling along Farm Road near Ferndown between 13:30 and 14:30 GMT on Thursday when a car hit the bicycle but failed to stop.
The car has been described as blue with "possibly pink wheels", Dorset Police said.
The victim, from Ferndown, regained consciousness and was taken to Poole General Hospital to be treated for what police described as "serious" injuries.
Police are appealing for witnesses or for information about the driver.
A cyclist was knocked unconscious in a hit and run in Dorset.