Abstract: In this study, a new simple and low-cost plastic optical fiber sensor for the measurements of low concentration HF vapors is described. The sensitivity to the HF vapors obtained by deposing a thin glass-like layer onto the PMMA core fiber after removing the fluorinated polymer cladding via dipping the fiber into ethyl acetate for a short period, not more than 40 second. Moreover, in order to enhance the fiber sensitivity, low pressure plasma treatments have been carried out in O2 and Ar gas mixtures, on polymeric optical core fibers in order to increase the core surface area without damaging the PMMA core fiber. The reaction of glass-like layer with the HF vapor alters the fiber light transmission and is detected by means of a wide-band photodiode. The sensor used in this research has several advantages; mainly the ability to evaluate directly the cumulative exposure and the transducer is based on a plastic optical fiber. The POF sensors are designed to monitor low concentration of gaseous pollutants in the RPC (Resistive Plate Chamber) muon detector of the Compact Muon Solenoid (CMS) experiment at the CERN in Geneva and also can be used both in civil and industrial field. Several prototypes of fiber sensors have been fabricated and characterized in the reaction chamber. The obtained results demonstrating the capability to detect low concentration of HF vapors with high sensitivity.