The LJP chief and minister for food, public distribution and consumer affairs was taken to the hospital after he complained of breathing problems.
A team of doctors is monitoring his condition, reports said.
Last Wednesday, Paswan was mobbed by locals when he went to his constituency Hajipur in Bihar to assess the flood situation.
Media reports say the minister was surrounded by a crowd after and was asked where he was for the last five days.
Locals in the flood-affected region complained about receiving no help from the government in assuaging their hardships.
More details are awaited about his health condition.