New thia-and diselena-crown ethers containing two suffer and selenium donor atoms have been prepared. And then, mercury (Hg^2+) ion-selective electrodes with PVC-plasticizer (STPB) based on some macrocycles as neutral carriers were also made. The electrochemical selectivities for various ions, and the effects for macrocycles, matrix of membranes, ratio of plasticizer to macrocycles, concentration and pH of test solution were investigated on the Hg^2+ ion selective electrodes. The 1,10-diselena-l8-crown-6-PVC-STPB (sodium tetraphenylborate) exhibited good linear responses of 28.2 ± 0.6 decade^-1 for Hg^2+ ion in the concentration ranges of 10^-2∼10^-6 M Hg^2+ ion. This electrode exhibited comparatively good selectivities for Hg^2+ ion in comparison with alkali and alkaline earth metal ions, some heavy metal ions and rare earth metal ion in the range of pH 2.5∼6.0. In addition, this electrode was applied as a sensor in the titration of Hg^2+ ion with I^- ion in water.