In order to enhance citric acid production by Yarrowia lipolytica 57, mutation and selection treatments were performed by using UV-irradiation and/or ethyl methane sulfonate (EMS) as a chemical mutagen. Totally 18 mutant strains were demonstrated by testing of 1,234 colonies and then used in citric acid production studies. Chemical mutagenesis was found as more effective in enhancing citric acid production than UV-induced mutagenesis. Maximum citric acid concentration (50.1 g/L) and yield obtained by the chemical mutant Y. lipolytica K-168 exceeded that of the initial strain by 57%. Growth and citric acid production of this strain was further examined in natural fermentation media containing carrot juice or celery byproducts. Maximum citric acid concentration reached to 62.6 g/L in diluted carrot juice medium supplemented with glucose. It was determined that enriched carrot juice may serve as a good nutrient source and could be used for citric acid production by K-168 strain.