Binary neutron star (NS) mergers are promising sites for the rapid neutron capture nucleosynthesis (r-process). The radioactive decay of synthesized elements powers electromagnetic emission called a kilonova. The detection of gravitational waves from an NS merger GW170817 and the observations of the associated kilonova AT2017gfo have provided us with evidence that r-process occurs in the NS merger. However, the abundance pattern synthesized in this event, which is important to reveal the origin of the r-process elements, is not yet fully understood. In the talk, I will present our recent results for identification of elements in the kilonva spectra a few days after the merger. We found that only several elements are important for absorption features, Sr, La, Ce, Gd, and Th, and some of them can explain the observed features in the spectra. We also confirmed our results of identification by utilizing stellar spectra. The direct identification of elements allows us to constrain amounts of synthesized elements.