This paper presents a new thin-film liquid salinity sensor by using the D-shaped fiber and thin-film coating techniques. The D-shaped fiber will enhance optical fiber to generate an evanescent field in sensing applications. Indium-galliumzinc oxide (IGZO) films can produce high attenuation lossy mode resonance (LMR) to make high-sensitivity liquid salinity fiber sensors. IGZO thin film is prepared by a radio-frequency (RF) magnetron sputtering method. The optical fiber thickness is 67.6 μm and IGZO film thickness of 100 nm is deposited on the polished surface of the D-shaped fiber to fabricate LMR-type liquid salinity sensors. The sensitive region was immersed in different sensing liquid salinities from 0 ‰ to 100 ‰, and attempted to investigate the sensitivities of the LMR salinity sensors. The experimental results show that the highest sensitivity of the salinity sensors for the sensing NaCl solutions is 0.80 nm per salinity unit (SU).