The upper and lower boundary conditions are important in theoretically modeling the height distributions of minor neutral constituent concentrations in the upper atmosphere by solving continuity equations. This paper discusses the effects of such boundary conditions on their concentrations. It is shown that the upper boundary condition of no diffusive flux at 150 km does not affect seriously the minor constituent density distributions except for H and HO2 above ∼120 km, where the escape flux of H reduces their concentratibns substantially. It is also shown that our previous model calculations have used the condition of constant flux with height at the lower boundary. It is suggested that reliable measurements of minor constituents in the upper stratosphere may be useful in improving the lower boundary condition for the mesosphere models and in simplyfying the modeling procedures.