The radiative transfer theory is used to solve the problem of thermal microwave emission from a homogeneous layer containing spherical scatterers. To model volume scattering effects, we use the Mie phase functions. To model rough top and bottom interfaces, we use the bistatic coefficients for a randomly rough surface obtained using a combination of Kirchhoff theory and geometrical optics approach. Because the bistatic coefficients violate energy conservation, there is ambiguity in the emissivity. However, using two alternate formulations, the upper and lower limits of the emissivity are calculated. The effect of a rough surface is incorporated into the radiative transfer theory by modifying the boundary conditions for the intensities. The radiative transfer equations are then solved numerically by using a Gaussian quadrature method, and the results are illustrated by plotting the brightness temperatures as a function of observation angle for different polarizations. It is shown that the presence of a bottom rough surface increases the brightness temperature except at high angles for vertical polarization. The rough surface at the top boundary makes the angular behavior flatter and displays smaller differences between the horizontal and vertical polarizations.