Almost constant lithium abundance in metal-poor stars ([Fe/H]<-1.5) has been interpreted as reflecting the product of the Big Bang nucleosynthesis. Observations of stars with less metal content ([Fe/H]<-2.5) have, however, cast doubts on this interpretation: lithium abundances show larger scatter, lowering the average value toward lowest metallicity. Although the cause of low lithium abundances in some extremely metal-poor stars is yet unclear, the star-to-star scatter highlights the incompleteness of our understanding of the evolution of metal-poor stars, which is the basis of the Galactic archaeology, or understanding of the environment of the early universe. In order to find a clue, we have examined existence of any correlation of stellar properties, such as atmospheric parameters or chemical abundances, with lithium abundances among extremely metal-poor stars ([Fe/H]<-3), using new results of abundance analysis for 8 unevolved stars and the data from literatures. Our preliminary results suggest that there is no correlation, and hence, lithium is depleted independent from the environment of the star or its evolutionary status. However, in order to reach more clear conclusion, precise measurements of stellar parameters and abundances for larger number of extremely metal-poor unevolved stars are highly desired. Such sample will be increased by the ongoing surveys of metal-poor stars with low resolution spectroscopy, such as LAMOST, and their follow-up observations with high resolution spectrographs such as HDS on the Subaru telescope.