Effects of heavy metal ions Hg²⁺, Pb²⁺, Cd²⁺ and Cu²⁺ on the growth and PO₄-P and NH₄-N purification capacity of photo-synthetic bacterium Rhodopseumonas palustris were studied. When the concentration of Hg²⁺ at medium was 2×10^-6mol·L^-1, the growth rate of this strain became slow, and its growth was inhibited completely at concentration of Hg²⁺ of 4×10^-6 mol·L^-1. At the concentration of Cu²⁺ of 1×10^-6 mol·L^-1, its growth rate became slow. Its growth was inhibited entirely while concentration of Cu²⁺ was high up to 8×10^-6mol·L^-1 too. while the concentration of Cd²⁺ at medium was 4×10^-5 mol·L^-1, the lag phase of this strain was delayed, and the growth of this strain was inhibited completely while concentration of Cd²⁺ was 16×10^-5 mol·L^-1. But the growth rate of this strain was hardly influenced when the concentration of Pb²⁺ at medium was 8×10^-4 mol·L^-1. While the heavy metal ion at medium was below the concentration inhibiting the growth of this strain entirely, PO₄-P and NH₄-N purification capacity of this strain was hardly influenced.