A novel dithio derivatized macrotricyclic compound (cryptand) has been synthesized using high dilution technique by condensation of diaminodibenzo18-crown-6 with 2, 2′dithiobenzoyl chloride. The compound was characterized by elemental analysis, 1H NMR, 13C NMR and FAB-MS. PVC membrane electrode based on this macrotricyclic compound showed good selectivity for Hg2+ ion with a wide linear range of 1.0 × 10−6 to 1.0 × 10−1 M and a lower detection limit of 5.0 × 10−6 M with a calibration slope of 30.2 mV decade−1. The electrode response was stable in pH range 3–6. Electrode showed good selectivity for Hg2+ over other interfering metal ions. The electrode was then applied to direct determination of Hg2+ in water samples.