In this study, the contents of fixed ammonium (FA) and mineral components in three different particle sizes (clay, silt and fine sand) and bulk samples from Changchenggang and Quanshui profiles in Nanjing region were analyzed by Silva-Bremner method while clay minerals were measured by X-ray diffraction, then the relationship between FA content and particle content, as well as mineral kind were discussed. The results showed that: ①among the three particle sizes, clay content had the closest correlation with FA content with the correlation coefficients of 0.68 and 0.64 for two profiles respectively. ②for three minerals (illite, kaolinite and montmorillonite), which were dominant in clay particles, illite content had the closest correlation with FA content with the correlation coefficients of 0.50 and 0.49 respectively. ③in the bulk samples, illite content had the most significantly positive correlation with FA content with the correlation coefficients of 0.68 and 0.66 respectively. These results indicated that illite might be one of the most important carriers for the storage of FA in paddy soil of Nanjing region.