A method of obtaining vitamin D from shiitake includes a) adding ethanol to shiitake powder, followed by reflux extraction, to prepare a shiitake extract; and (b) irradiating ultraviolet (UV) light to the shiitake extract prepared in step (a). When shiitake extracts are obtained and exposed to ultraviolet light under specific conditions, the content of vitamin D2 in the shiitake extracts may be increased.