The purpose of this study is to investigate spatial coherence of superluminescent diode (SLD). In order to measure the spatial coherence, we use an interferometer with double slit. The relation between visibility of the fringe and the diffraction length are reported. Furthermore, difference in spatial coherence between SLD and LED is discussed.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.