We give here the calculation of the order parameter and the spontaneous polarization as functions of temperature using the mean field model close to the phase transitions in NaNO2. We have fitted our calculated order parameter to the observed one from the literature. From this fitting, we have then calculated the spontaneous polarization as a function of temperature close to the phase transitions in NaNO2. Our calculated spontaneous polarization is in good agreement with the observed spontaneous polarization reported in the literature. (C) 2001 Elsevier Science B.V. All rights reserved.