In an incubation study the comparative effects of different carbonaceous compounds on the immobilization and mineralization of phosphorus applied to the soil were investigated. Approximately 31.7% and 29.5% of added P in soils containing additions of glucose and starch was converted into organic P within 10 and 20 days of incubation respectively. Most of this converted organic P was found in the form of labile and moderately labile forms of organic P and both of these readily mineralized again leaving less than the native labile P fraction of the control treatment. In the case of cellulose and crude fibre additions, the immobilization started slowly and reached a maximum of 31.9% and 27.9% of applied P at 40 and 50 days of incubation respectively. More than 63% of the increased organic P was contributed by fulvic and humic P fractions which showed resistance to mineralization. Lignin did not show any significant effect on immobilization and mineralization of P in the soil. Cellulose, per gram of its carbon decomposition, had a higher capacity for immobilization than the other sources of carbonaceous compounds.