Rhizospheric fungi have an array of heavy metal–tolerating properties that allow them to be used as a bioremediation tool. Exploring the biosorption capacity of fungal biomass is an economical technique to mitigate arsenic from agricultural land. However, there are few studies enumerating the procedure required to understand the tolerance potential of fungal strains isolated from soils contaminated with arsenic. In this chapter, a protocol to calculate the tolerance index for arsenic in fungal isolates is described that helps in determining subsequent arsenic removal. Fungal isolates with a significant arsenic tolerance index can be used in agricultural lands to modify the rhizosphere microbiome as a solution to overcome the arsenic toxicity.