Vitamin A, whose active form in our body is all-trans-retinoic acid (atRA), is essential for normal embryonic development and many other biological functions. CYP26A1 is an isoform of cytochrome P450 enzyme which is responsible for atRA metabolism and elimination. Since we cannot synthesize vitamin A on our own, humans must consume vitamin A as nutrients. Because both too much and too little intake of the vitamin are detrimental, a tightly regulated feedback system controls the level of vitamin A circulating in the body. CYP26A1, which is shown to be strongly inducible by atRA, takes a major role in modifying atRA into its inactive forms. Common aryl hydrocarbon environmental toxins are also known to induce the activity of CYP26A1 by binding to aryl hydrocarbon receptor (AHR). My current work aims to increase the understanding of the effects of environmental toxin on CYP26A1 in comparison to its other isoforms. I treated HepG2 cell line with varying concentration of 3-Methylcholanthrene (3MC) for 24 hours and quantified the amount of CYP26A1 mRNA. The results show that 3MC induces CYP26A1 transcription up to a certain toxic concentration. With better understanding of how common environmental toxins affect the health of an individual at a molecular level, it is possible to mediate the effects of the environmental toxins.