A fiber ring cavity laser refractive index (RI) and temperature sensor is presented. A core-offset Mach-Zehnder interferometer is utilized as a sensing element as well as a filter. The Erbium doped fiber ring cavity laser setup is helpful to improve the spectral quality factor Q and the detection limit. The calculated detection limits of 0.35 °C and 4.54 × 10−4 for temperature and RI measurement are 10 times higher than the individual MZ interferometer.