In this study, an easy to construct and sensitive intracavity fiber loop ring down spectrometer was built by commercially available basic components and its application on chemical sensing is presented. System performance was investigated by using various acetylene/nitrogen gas mixtures as a function of total pressure (between 25 and 65 psia) in sensing region and a calibration curve is established. The instrument can achieve a limit of detection of 0.1% without a FBG and/or EDFA or a need for a complicated design. Moreover, the detection limit can be further improved by working at higher pressures. With the current design of the system, the change in type and/or concentration of species in the sensor region can be monitored in real time.