Magnetic field and temperature dependence of Sagnac interferometers consisting of birefringent magneto-optic fibers is investigated. Experimental results show that the transmission spectrum of the all-fiber Sagnac interferometer moves towards the shorter wavelength side with the increase in temperature (temperature coefficient -0.435 nm/℃), and the transmissivity becomes wavelength- insensitive for a larger magnetic induction. And then, the temperature-insensitive magnetic field measurement is achieved by adjusting the polarization controller within the interferometer, and the magnetic field coefficient is 189 mW/T2 in the experiment, which is in agreement with the theoretical results.