Inorganic Phosphate (Pi) is an essential nutrient for plant growth and development, however that most soils have in low availability. To overcome this problem it is necessary to apply high amounts of Pi fertilizers, however this is inefficient and costly. Recently, there is increasing interest in the use of rock phosphate (RP) and microorganisms capable of increasing its agronomic effectiveness as crop fertilizer. However, it is unclear the impact that some critical nutrients such as carbon (C) and nitrogen (N) may have on the effectiveness of the microbial RP dissolution. The aim of this study was to evaluate the effect of C and N source and concentration on the RP dissolution by the fungus Mortierella sp. under in vitro conditions. The results indicate that the efficiency to dissolve RP was significantly higher with glucose, followed by arabinose; other sources were ineffective (fructose, sucrose, maltose, cellulose and molasses). On the other hand, NH4Cl was significantly the most effective N source, followed by NH 4 NO 3 . By contrast, KNO3 was ineffective to promote RP dissolution. The best concentration of glucose was 10 g L -1 , while for NH4Cl it was 1 g L -1 . These findings show that by varying nutrient supply, the RP dissolution reactions can be significantly enhanced.