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We demonstrated a fiber-optic sensor using spheroidal-cavity-overlapped fiber Bragg grating (FBG) for simultaneous temperature and strain sensing. The spheroidal cavity is fabricated through splicing two sections of the photon-sensitive fiber together and located in the center of the FBG to act as a Fabry–Pérot interferometer (FPI). Experimental results demonstrate that the temperature sensitivity of the FPI part of the sensor is 0.67 pm/°C at the range of –70 °C–20 °C, and its strain sensitivity is 3.76 \mboxpm/\mu\varepsilon at the range of 0–500 $\mu\varepsilon$, while those of the FBG part are 8.40 pm/°C and 1.40 \mbox{pm} /\mu\varepsilon, respectively. The sensitivity difference ensures good simultaneous measurement performance. [ABSTRACT FROM PUBLISHER]