For body inner temperature measurement, especially for tumor hyperthermia temperature real-time monitoring, temperature sensing probes should have smaller volume, good toughness and resistance to electromagnetic interference ability. This paper focuses on a medical small optical fiber grating temperature sensing probe. The glass tube was used to encapsulate short fiber Bragg gratings to allow the probes to effectively avoid the error caused by stress and to eliminate the influence of metal packages on the distribution of electromagnetic field. Meanwhile, the probe and fiber were wrapped in medical polyurethane sleeve to effectively protect the probe and fiber and make them be good toughness. After packaging, the cross-section diameter and the length of the probe are 1 mm and about 4 mm, respectively. The reflection wavelengths of the probe at different temperatures, the response time of the probe at changed temperature and the internal temperature change process of the pork heated by the medical radiofrequency hyperthermia machine were measured experimentally. The results show that the linear correlation coefficient between the reflection wavelength of the probe and the temperature is 0.999 95 in the body temperature range. The temperature sensing accuracy and the maximum response time of the probe is 0.2 ℃ and about 4 s, respectively. Moreover, the probe can be used to monitor the internal temperature change of the pork heated by the medical radiofrequency hyperthermia machine in real-time.