Citric acid is known as one of the most important organic acids produced by microbial fermentation. Aspergillus nigerhas remained the fungus of choice for citric acid production. Our study is concerned with optimizing the conditions for the highest production of citric acid by A. niger isolated from different natural sources. Aspergillus nigerwas isolated from fresh orange fruits and soil. They were screened for their citric acid productivity at different conditions. The obtained results showed that of the highest production citric acid by both fungi was achieved at pH 5.0 and 6.0 respectively, temperature 30 0C, inoculum size 1%, and incubation period of 168 h. Also, the maximum amount of citric acid produced by the two fungi was demonstrated at molasses containing medium (15 %). Hence, Cane molasses was selected as the best carbon source for the further study. Moreover, it was found that citric acid production by immobilized spores of both fungi was higher than the free ones.