Abstract: Portuguese oyster larvae were exposed to solutions of K⁺, Ca²⁺, Mg²⁺ and NH₄⁺ at various concentrations. The result was showed below: At the beginning of the test, K⁺ and NH₄⁺ induced larvae settlement behavior. After a week, except Mg²⁺ and NH₄⁺, under the concentration of 10 mM,20 mM, K⁺ and 10 mM~25 mM, Ca²⁺ both induced larvae settlement and metamorphosis; NH₄⁺ caused high mortality. This indicated that in commercial breeding of Portuguese oyster, K⁺ and Ca²⁺ might be the potential chemical cues.