Electric current measurement has become an important aspect in electric current quality monitoring. In the development of electric technologies, electrical system needs new current measurement technology with high sensitivity and resolution. In this study, an optical fiber current sensor has been developed using SMS fiber structure and ferrofluid for an alternating current measurement. This optical fiber current sensor works with the change of refractive index of ferrofluid. Ferrofluid is colloidal suspension that is made from Fe3O4 nanoparticle and surfactant (oleic acid, citric acid, etc). The refractive index of ferrofluid will change due to the magnetic field that affects ferrofluid. The experiment was done by measuring the change of output power of optical fiber current sensor using Optical Power Meter due to current flow in the wire. The alternating current range used in this study is 0-10A. The results show that the SMS fiber current sensor has a sensitivity of 3.049dB/A in the range 2-7A, 95% of precision rate and a resolution of 0.037A.