We have proposed a method to determine the focal length of microlens array (MLA) based on the measurement of transverse displace- ment of image spot in the focal plane for a change of angle of incidence of plane wavefront. An existing interferometer test setup, meant for the sur- face figure measurement of MLA substrate, along with a charge-coupled device (CCD) is used for this purpose. The interferometer generates as well as measures the angle of incidence of plane wavefront at the MLA, and the transverse displacement of the image spot is determined from images recorded with the CCD. We have also discussed the theory of estimation of the focal length of MLA with spherical wavefront. Error analysis is carried out for both methods and is compared. The proposed plane wavefront method is experimentally demonstrated with an off-the- shelf MLA, and the measured focal length is within 1% of catalogue value. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1 .OE.52.12.124103)