Heavy metal pollution is one of the most important environmental problems today. It brings about serious environmental pollution, threatening human health and ecosystem. Conventional methods for removing metal ions from aqueous solution have been used such as chemical precipitation, filtration, ion exchange, electrochemical treatment, membrane technologies, adsorption on activated carbon, and evaporation. Alternative process is biosorption, which utilizes various certain natural materials of biological origin, including bacteria, fungi, yeast, and algae. This study evaluated the potential of Candida tropicalis yeast strain as a bio sorbent agent for mercury (Hg). Distilled water contaminated with mercury having an initial concentration of 0.003ppm was used to measure the optimum contact time of the yeast strain and heavy metal for the biosorption to be effective. The biosorption capacity of the test organism was determined post treatment at 24, 48, and 72 hours. The contact time having the largest decrease of mercury concentration determined the optimum biosorption activity of the yeast strain to Hg. Largest decrease in Mercury concentration determines which time the biosorption of yeast strain with Hg was at the optimum level. Results demonstrated that the level of Hg in contaminated water at seventy two hours post treatment was significantly lower by a mean value of 0.00033ppm. This means that biosorption of dissolved Hg was optimum in 72 hours treatment with yeast strain, Candida tropicalis. Therefore, 72 hours is the best contact time needed for the biosorption of Hg by the yeast strain.