Balanced and unbalanced Mach-Zehnder interferometers were developed using two photoresist gratings fabricated on slide glass substrate. One grating served as the beam splitter and the other as the beam recombiner. A laser beam was incident on the first grating to produce multiple diffracted beams. The balanced interferometer used two mirrors to reflect two symmetrical diffracted beams onto the second grating, making the two patterns diffracted by the second grating completely superposed. The phase difference between the two components of one of the superposed beams was measured with a photodetector. For the unbalanced interferometer, only one diffracted beam was reflected upon the second grating, producing a diffraction pattern that completely overlaps with that from the zeroth-order beam. Performance of the unbalanced interferometer was investigated by using a 50 μm-thick glass plate to induce the phase difference.