The single continuum model formulation, no matter how complex the considered constitutive relations are, cannot describe important phenomena stemming from constituents’ interactions. In contrast, mixture theory is a successful framework for providing thermodynamically consistent governing equations in the bulk allowing for the inclusion of details in the material structure and interactions. Despite its ubiquitous applications, a fundamental open problem, a framework for the assessment of boundary conditions, persisted.Our objective is to relate these boundary conditions of mixtures to those of a single continuum and, hence, derive their possible form. To obtain such an estimation, we suggest using the Maximum Entropy (MaxEnt) principle yielding the least biased estimate (when measured by the entropy) of the values of the state variables on the more detailed level based on the knowledge of the state on the less detailed level. In the case of mixtures, the total mixture quantities represent the less detailed description, whereas the quantities related to each phase of the mixture represent the more detailed level, and the mapping (projection) connecting the two levels usually follows from the conservation of total mixture quantities. Therefore, once we have entropy on the detailed level and the aforementioned projection, from the MaxEnt principle, we get the least biased estimate of the decomposition of the total mixture state variables into variables corresponding to each constituent.These estimates can be used to obtain the interfacial conditions between two mixtures: we consider the decomposition of the total mixture quantities to partial quantities on both sides of the interface independently and match the mixture quantities at the interface using classical boundary conditions for a single phase. In this way, we may connect the well-developed theory for single continuum boundary conditions to the boundary conditions in mixtures. The generality of such an approach is discussed together with an explicit example of a binary system of ideal gases illustrating the whole procedure explicitly. The outlined MaxEnt procedure results in a decomposition of total pressure in accordance with Dalton’s law of partial pressures in a mixture of ideal gases. Finally, we apply the method numerically to a mixture of van der Waals gases demonstrating the versatility of the proposed framework. We obtain a nontrivial prediction which differs from the decomposition of mixture pressure according to Dalton’s law.