Loranthus tanakae is a deciduous shrub within the family Loranthaceae, and mostly parasitizes plants within the family Fagaceae. This study aimed to investigate the population growth and spatial distribution patterns of L. tanakae and its major host plant Quercus wutaishanica, and the parasitic behavior of L. tanakae in the Loess Plateau. The results showed that 42.1% (i.e. 358/851) of the sampled individuals of Q. wutaishanica were parasitized, with the number of parasites (L. tanakae) per host plant ranging from 1 to 20. Q. wutaishanica displayed a clumped pattern of spatial distribution at the scale of 0-60 m and a random pattern at the scale of ≥60 m, while L. tanakae showed a clumped pattern of spatial distribution at the scale of 0-100 m. 85.1% (i.e. 964/1112) of parasitic L. tanakae were observed within the 1/2 topheight of Q. wutaishanica, and the haustorium size of the hemiparasite was significantly associated with the circumference of the infested branch (r=0.713, P<0.01). Individuals of Q. wutaishanica with greater height and larger crowns were found to be more susceptible to the infection, and L. tanakae tended to parasitize the upper portions of the host plants.