In　recent　years,　the　reactive　wetting　of　Ni-Si　on　graphite　has　attracted　increasing　attention.　However,　most　attention　has　been　focused　on　the　effect　of　Si　on　the　wetting　behavior　of　Ni-Si/C　systems.　In　this　work,　the　wetting　process　of　Ni-Si　alloys　with　different　Si　content　(20,　28,　35,　45　and　55　wt%)　on　graphite　substrates　has　been　investigated　at　1523　K　in　a　high　vacuum　using　a　modified　sessile　drop　method.　The　threshold　activity　of　Si　in　liquid　to　form　SiC　at　1523　K　can　be　calculated　to　be　0.0173,　corresponding　to　a　Si　content　of　33　at%　(19　wt%).　In　addition,　a　minimum　equilibrium　contact　angle　of　20°　can　be　observed　in　the　Ni-45　wt%　Si/C　system.　The　adsorption　energies　of　Si　at　the　interface　and　at　the　surface　of　the　Ni　metal　are　5.36　kJ　mol-1　and　-20.9　kJ　mol-1,　respectively;　whereas,　the　adsorption　energies　of　Ni　at　the　interface　and　at　the　surface　of　the　Si　metal　are　-5.38　kJ　mol-1　and　68.9　kJ　mol-1,　respectively.　Moreover,　the　effects　of　Si　and　Ni　on　the　change　in　the　equilibrium　contact　angle　have　been　evaluated　in　terms　of　the　solid-liquid　interfacial　energy　and　the　surface　energy　of　the　liquid　alloy.　©　The　Royal　Society　of　Chemistry　2015.