The grain boundaries (GBs) in continuous films or domains of MoS 2 are vital to its optical and electrical properties. Almost all previous approaches for GBs visualization are based on microscopy and spectroscopy and only effective for domains with less than several micrometers in size. Here we report a simple method for the visualization of large GBs in MoS 2 surface by optical microscope. Gold was deposited on the MoS 2 grown by chemical vapor deposition, and then the GBs could be observed by

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... optical microscope. Upon gold deposition on MoS 2 , the entire GBs of large-area MoS 2 were clearly visualized using this method. To verify the result, the GBs were also characterized via scanning electron microscopy, transmission electron microscopy and atomic force microscopy. It showed the small particles of gold were clustered together on GBs, which had a larger binding energy than the inner regions. The method is universal and allows for the nondestructive identification of the GBs in any two dimensional materials with large area.