This study introduced an optical fiber core sensor designed to measure chloride ions by removing the fiber's coating and cladding, allowing direct interaction between the fiber core and external solutions, thereby enhancing measurement sensitivity. Two types of fibers, plastic and quartz, were evaluated for their efficacy as sensors. Experimental results demonstrated that the fabricated plastic core fiber failed to accurately reflect alterations in external solutions onto the spectrum, making it unsuitable for sensor applications. Conversely, the quartz fiber core, when treated with chloroform to dissolve its cladding, exhibited superior performance due to its wider transmission wavelength range and higher durability. The integration of a silver film on the core further improved the sensor's sensitivity through surface plasmon resonance. The study also explored the impact of thin-film and thick-film formations on sensor performance, with the thin film providing rapid response times and the thick film offering enhanced durability. This advancement holds significant potential for applications in environmental monitoring and the early detection of chloride-induced corrosion in various structural materials.