A novel Sagnac interferometer employing an optical fiber grating in its loop is presented.The transmission responses of the loops with uniform Bragg gratings an d linearly chirped fiber gratings are calculated. The analytic expressions for the loop with a uniform Bragg grating are given. It is found that the loop of a u niform grating leads to equally spaced band-passes,while that of a chirped fiber grating leads to unequally spaced band-passes. Such Sagnac loops may find appli cations in dense wavelength division multiplexing (DWDM) systems and optical fib er sensing. The multiple band-passes filters with 8 and 16 channels are demonstr ated experimentally. The experiments verify the results of our analysis.