The crash happened at about 7.20am on the A639 Barnsdale Road between Methley and Castleford.
The road is closed in both directions, between A6032 Methley Road and Green Lane, as officers investigate the crash.
A spokesperson for West Yorkshire Police said: "At 7.22am today police were called to a report of a serious road traffic collision on the A639 between Methley and Castleford involving a van and cyclist.
"The cyclist, a male, was taken to hospital with serious injuries and remains in a serious condition at this time.
"The road remains closed in both directions at this time and enquiries regarding the circumstances of the collision remain ongoing."