Abstract: Disclosed are a method and apparatus for detecting the content of oleic acid by optical fiber, and manufacturing method of the apparatus. By the principle of Surface Plasmon Resonance (SPR), a metal layer in a sensing region excites an analyte of oleic acid to produce a plasmon resonance, and a physical property of the plasmon resonance such as a resonant wavelength is measured to define the concentration of oleic acid of the analyte, so that the present invention can measure the concentration of oleic acid accurately and quickly to reduce the time and cost of detecting the oleic acid effectively, so as to improve the efficiency of detecting the oleic acid.