A miniature in-fiber Fabry–Perot interferometric (FPI) sensor is demonstrated. Through manufacturing microhole in a single-mode fiber with excimer laser, a single microhole FPI sensor and a dual microhole FPI sensor are fabricated, and the temperature sensing characteristics of them are investigated experimentally. The results show that the spectra of two sensors shift to short wavelength with an increase in the temperature, and the relationships between wavelength shift and temperature change have better linearity in temperature range of 30°C to 85°C. The temperature sensitivity of single microhole FPI sensor is 0.160 nm / ° C, and the dual microholes FPI sensor has two temperature sensitivities corresponding to different FP cavities. Furthermore, the temperature sensitivity can be adjusted by changing the distance between two microholes. When increasing the distance from 1 to 2 mm, the higher temperature sensitivity can be changed from 0.176 to 0.192 nm / ° C, and the temperature-dependent wavelength shift still keeps a good linearity. Compared with conventional fiber Bragg grating temperature sensor, this kind of FPI sensor has not only different dual temperature sensitivities but also higher sensitivity and stability, so that this kind of microhole FPI sensor can be used in many fields.