Novel sol-gel processing techniques of ceramic materials were developed for designing new functional environmental ion sensors. Wet-chemical preparation methods for metal-oxide thin-films, perovskite-type oxide thin-films, and solid-electrolyte discs could be developed by using solution techniques based on polymer precursors, etc. New electrochemical sensing techniques to hydrogen-phosphate ion with high sensitivity and selectivity were developed by the use of ceramic-based sensors. A sol-gel processing technique was developed for the preparation of La-based perovskite-type oxide thin-films using an acetylacetone (AcAc)-modified poly(vinyl alcohol) (PVA)-based polymeric precursor method. The AcAc modified PVA-based sol made it possible to deposit a thin-film as well as to lower the sintering temperatures. The La0.8Sr0.2CoO3 perovskite-type oxide thin-film electrode prepared at 500°C showed good properties of amperometric sensing to hydrogen-phosphate ion. A new solid-electrolyte ion sensor device using a Na+-ion conductor (Na5DySi4O12: NaDyCON) as an impedancemetric transducer and a perovskite-type oxide thin-film as a receptor has been further developed. The AC impedance of the device with a LaCoO3 receptor was found to vary logarithmically with increasing K2HPO4 concentration between 1.0 x 10-5 and 1.0 x 10-2 M at 10 kHz. The 90% response time was ca. 2 min at room temperature. The sensor showed a little sensitivity to NO3- at higher concentration, while no response was observed to the examined anions of Cl- and ClO4-.