This paper presents the simultaneous measurement of strain and temperature using Fiber Bragg grating/extrinsic Fabry-Perot interferometric (FBG/EFPI) sensor. This hybrid sensor consists of a FBG element encapsulated in EFPI sensor. Temperature can be measured from FBG part and strain from EFPI. We have analytically derived the relationship of the sensor outputs to measurands (strain and temperature) and yielded the characteristic matrix of sensor. Therefore, it is not necessary to perform sensor calibration for each sensor. By the derived relationship, we could measure directly and simultaneously the strain and temperature using a single sensing element. The fiber optic sensor was surface-mounted on an aluminum alloy beam together with an electrical resistance strain gauge and a thermocouple. The wavelength-swept fiber laser (WSFL) was used as a light source to supply high signal power. The simultaneous measurement of thermal strain and temperature was performed in a thermal chamber. Experimental results of Fiber optic sensor show good agreements with those of conventional gauges such as strain gauge and thermocouple.