Abstract: The potential stripping behaviour of Cu(Ⅱ) and Sn(Ⅳ) in cysteine solution was studied in detail. Sensitivities for the analyses by APSof the two elements in this system may be increased by 1-2 orders of magnitude under optimum conditions (forCu(Ⅱ):0.50M NaCl, pH3.0, 2×10^-4M GysH, E_d-0.90V; for Sn(Ⅳ): 0.40M NaNO₃, pH2.9, 3×10^-4M CysH, E_d-l.10V), with the variation coefficients 2.6% and 1.4% separately.It was observed that with co-existance of Cu(Ⅱ), cysteine also gave well-defined potential stripping waves which may be used to determine cysteins. Uader optimum conditions (0.50M NaNO₃, pH2.8, 1×10^-5M Cu(Ⅱ), oxidate. Hg(Ⅱ),the transient time(τ) is proportional to cysteine concentration in the range of 2×10^-10-1×10^-5M, with the variation coefficient 2.5%.