Bi-capacities have been presented recently by the authors as a natural generalization of capacities (fuzzy measures). Usual concepts as Möbius transform, Shapley value and interaction index, Choquet integral, kadditivity can be generalized. We present formulas of the Choquet integral w.r.t. the Möbius transform, and w.r.t. the interaction index for 2-additive bi-capacities.