Nitrogen (N) is one of the most important volatiles in terrestrial atmospheres and plays a key role in planetary habitability. After Earth's completion of the core-formation, the exchange of N between the proto-atmosphere and the last magma ocean (MO) through N-ingassing or -degassing governed the distribution of N between the proto-atmosphere and the silicate MO, setting up initial conditions for the subsequent evolution. At a given N mass in the proto-atmosphere and the last MO, N2 solubility in the silicate MO would determine the partial pressure of N2 () in the proto-atmosphere and the N concentration in the MO. During crystallization of the silicate MO, N2 solubility in the solidifying MO, N partitioning between solids and the residual melts, and the retention of silicate melts in the solidified mantle would reset the distribution of N between the proto-mantle and the proto-atmosphere. In these processes, a larger N2 solubility in the silicate MO would imply more N dissolved in the silicate MO and the proto-mantle but a lower in the proto-atmosphere; and vice versa. We perform a series of high-pressure experiments to determine physical N2 solubility in silicate melts with compositions spanning from basalt toward the mantle peridotite at 1-2.5 GPa and 1200-1600 ℃. Our preliminary results show that N2 solubility measured by SIMS and EMPA ranges from 400 to 2800 µg/g, increasing with increasing pressure but decreasing with increasing the silicate melt NBO/T. Using our measured pressure and compositional dependence of physical N2 solubility, we will test the accuracy of previous N2 solubility models, and we then discuss the behavior of N in the MO and its distribution between the proto-mantle and the proto-atmosphere.