A Liquid-Core Waveguide (LCW) detection system for high sensitive determination of tegaful (FT) was developed. In this system the LCW cell was connected to the end of a hollow cathode lump and the other end to a UV spectrometer. A sample solution containing FT was pumped to the LCW cell through a T-shaped connector. A UV absorption of analyte was detected by the UV spectrometer. The configuration of connectors of LCW cell to the light source and the UV detector was designed. Stable and high responses of FT were obtained in a double tube system in which an edge of LCW cell was covered with another tube with large diameter was set in the T-connector. It was found that the UV absorption response of FT obtained in this LCW system depends on the core length and the concentration of FT. The sensitivity of FT obtained by using 65 cm of the LCW cell length was 10-fold higher than that of using 1 cm cell which was often used with a conventional UV-visible detector.