The measurement of power by conventional meters has some limitations due to the inductance and capacitance of coils and the eddy current induction in the metal parts of the meters. Optical fiber gratings are currently being used as sensors for a number of physical quantities such as temperature, strain and pressure; other quantities, such as current and electrical power measurements can be detected by fiber gratings using appropriate transducers. This paper demonstrates an optical fiber sensor using a Fiber Bragg Grating (FBG) and a piezo-electrical transducer (PZT) to measure real and reactive powers. Mounting an FBG on a PZT bar, a dynamic strain simulator is constructed. The voltage equivalent to the product of load voltage and load current applied on PZT is converted to the dynamic variation of the FBG Bragg wavelength. The load power will be achieved by measuring the changing value of the wavelength. A phase detector circuit is used to measure the phase angle between voltage and current signals. The power factor can be obtained from the phase angle. Thus, the sensor can be used to measure real and reactive powers without the use of a traditional power meter.