A microfluidic system for chloride ion measurement using a long-period fiber grating (LPFG) is presented. Optical fiber sensors based on waveguide technology are promising and attractive in chemical, biotechnological, and civil engineering applications. The LPFG-based microfluidic system used to measure the transmission powers of different chloride ion concentration solutions of sea sand and seawater. The results show the relationship between transmitted light intensities and different chloride ion concentration solutions was close to linear. This system could be potentially used to discriminate the different chloride ion concentration solutions. This LPFG-based microfluidic system for chloride ion measurement reported here could hopefully benefit the development and applications in the field of civil engineering especially for concrete and raw material testing as well as infrastructure health monitoring.