Organic manure is one of the sources of nitrogen in the soil. Nitrogen mineralization depends on application method, source of organic manure, microbial activity, aeration and moisture. The objective of this study was to investigate the rate of nitrogen mineralization as affected by different sources of organic manures (compost, chicken manures, and town refuse) which mixed with clay and sandy soils at the rate of 10 and 20 t fed^-1 at different incubation periods. The experiment was carried out in laboratory of Soils Department, Faculty of Agriculture, MansouraUniversity. Soil samples were taken from El-Mansoura (clay soil) and El-Sharkia (sandy soil). Nitrogen mineralization was studied in both soils mixed with different organic manure types at different incubation periods. The analysis of ammonium and nitrate were conducted at (0, 7, 14, 30, 60 and 90 days after incubation at 38˚C). The results showed that NH₄⁺-N content at the different organic manures application to both soils used increased compared with the control (without organic manure addition) at different incubation periods. The maximum concentration of NH₄⁺ -N obtained at 60 day of incubation with compost then chicken manure in sandy soil and contrast with clay soil. While the maximum concentration of NO₃^--N reaches at 90 days after incubation in both soils It was clearly with compost then chicken manure in clay soil and contrast with sandy soil. It can be concluded that, nitrogen mineralization is the process by which organic N is converted to inorganic forms which mostly ammonium (NH₄⁺) and nitrate (NO₃^-). When manures are regularly added to soils, the mineralization gradually increases over time until it eventually reached a plateau know as the steady-state condition.