The accident happened last night, they said adding the victims were travelling to Nagaur district to attend a wedding ceremony.
Dalpat Singh along with his family was on way to Nagaur when their car hit a static truck, 70-km from here, police said.
Four, including three siblings aged between seven and 13, died at the scene, they said.
The three siblings are the children of Dalpat Singh who himself was injured in the accident along with his wife and another son.
Dalpat was in serious condition in hospital, police said.