The paper presents a method based on beat frequency analysis for measuring key characteristics of a liquid sample, such as its refractive index and concentration. The measurement process was implemented using dual-path optical feedback self-mixed interferometry. The proposed method was validated through a comprehensive experimental study on various concentrations of NaCl-H₂O solutions. The study concludes that the process can detect a minimum concentration of 0.1% and shows strong agreement with the true concentration values. Additionally, the method demonstrates excellent precision, on the order of 10−5, in refractive index measurements. Consequently, the authors envision this measurement method as a simple, cost-effective, and compact solution for liquid refractive index and concentration measurements.