Abstract: We int roduced the theory and methodology of Resource Selection Functions (RSFs) , and used a RSF to analyze nest site selection of Crested Ibis ( Nipponia ni ppon) . We compared the results of the RSF with those of principle component analysis (PCA) , and found that both methods indicated that habitat factors such as area of rice paddy , height of nest t ree , elevation and human disturbance played important roles in nest site selection. Nest orientation , coverage above the nest , aspect and slope of the hill where the nest tree was located were also not important . However , there were significant differences between the two methods. The RSF showed that the position of the nest t ree on the slope greatly affected nest site selection , and PCA indicated that the t ree density was more important .After detailed comparison , we concluded that RSFs are better than the commonly used PCA in studying habitat selection. We also discuss issues about how to select cont rol plot s and the independence of parameters while using RSFs. Finally we offer some suggestions for the conservation of Crested Ibis.