Abstract Based on the first-principles calculation, we investigated Cr segregation behavior at the C11b/C40 lamellar interface for MoSi2-based alloys. We first elucidated the energetically stable interface structure among possible contacts between C11b and C40, where the interface energy is 1.7 meV/Å2. Without inclusion of lattice vibrational contribution to segregation energy, Cr composition at the interface was lower than that at C40 phase, which was inconsistent with the early experimental result. Inclusion of the vibrational contribution successfully resulted in strong Cr segregation at the interface over that at C11b as well as C40 phase. This indicates that Cr segregation at the most stable interface is a thermodynamically stable state, in which lattice vibration plays a significant role.