A method for measurement of refractive index profile of a GRIN system is developed based on a longitudinal interferometer using a birefringent lens (BL). The fringe pattern so generated is made to traverse through the sample under test. The modification of the fringes gives a measure of the refractive index profile. The fringe patterns both in presence and absence of the test samples are grabbed by a CCD camera and further processed by a computer. The basic software required for the same is being developed. Some experimental results are presented © 2001 SPIE · 0277-786X/01/$15.00.