Abstract A comparison of the rain rate estimated with the assumptions of Rayleigh and Mie scattering is made. We analyzed the different relationships between the radar reflective factor and rain rate (so-called Z– R relationship) with both scattering models for different DSDs (droplet size distributions) and rainfall types as the wavelength is 2.2 cm which is in accord with the band of TRMM/PR. Meanwhile we introduced a discrete ordinates method to retrieve the Z– R relationship for Mie scattering assumption. It is found that the retrieval result can be represented as the sum of some simple Z– R relationships. By the analysis of the Z– R relationships estimated from Rayleigh and Mie scattering assumptions in the rain types, we found that the difference of Z– R relationships between Rayleigh and Mie scattering in the thunderstorm that represents the larger raindrop size is larger than that in the drizzle that represent the smaller raindrop size.