The reduction of Bi(III) with Arginine and Leucine is investigated polarographically in aqueous medium. Bi(III) formed 1:1, 1:2 and 1:3 complex species with Arginine as well as Leucine. The stability constants of Bi(III) with Arginine and Leucine were measured by the method of DeFord and Hume. The reduction of the system in each case is quasireversible and diffusion controlled, involving three electrons. The thermodynamic parameters have been determined. The stability constants of these species at 300K for Bi(III) with arginine are logb₁ = 1.93, logb₂ = 3.90, logb₃ = 6.39 and at 310 K are logb₁ = 2.11, logb₂ = 4.04, logb₃ = 6.30 and thermodynamic parameters free energy (KCal mol^-1), enthalpy (KCal mol^-1) and entropy (Cal mol^-1 deg^-1) are -2.53, -46.52 and -0.14 (MX₁), -5.12, -44.84 and -0.12 (MX₂), -8.39, -41.95 and -0.11 (MX₃) respectively. The stability constants of these species at 300K for Bi(III) with Leucine are logb₁ = 1.77, logb₂ = 4.00 logb₃ = 6.38 and at 310 K are logb₁ = 1.76, logb₂ = 3.95, logb₃ = 6.25 and thermodynamic parameters free energy (KCal mol^-1), enthalpy (KCal mol^-1) and entropy (Cal mol^-1 deg^-1) are -2.32, -42.31 and -0.13 (MX₁), -5.25, -42.02 and -0.12 (MX₂), -8.37, -41.68 and -0.11 (MX₃), respectively. The Mathematical Mihailov's method has also been applied for the comparison of stability constants values obtained by graphical method.