Parasitic biology of Pedicularis L. (Orobanchaceae) has been underinvestigated despite its wide distribution and potential ecological significance. To better understand the parasitic aspects of the root hemiparasites, host-parasite interactions were investigated with two sympatric Pedicularis species, Pedicularis rex C. B. Clarke and Pedicularis tricolor Hand.-Mazz., at two developmental stages. Plant DW, shoot phosphorus (P) content, root : shoot ratio and number of haustoria were measured in Pedicularis grown with either a host plant or a plant of its own species in pot experiments. In addition, effects of parasitism and intraspecific competition on growth and biomass allocation in four host species belonging to three major functional groups (grasses, legumes and forbs) were investigated. The two Pedicularis species showed obvious host preference, but preferred different host species. Interactions between Pedicularis and their hosts depended on both species identity and developmental stages of the partners. Overall, P. rex showed much weaker host dependency and less damage to hosts than P. tricolor. Interspecific variations were observed among different host species in their responses to intraspecific competition and parasitism. We concluded that different Pedicularis-host pairs showed different interaction patterns. Sympatric Pedicularis may have differential influence on plant community structure and productivity.