In order to investigate the optimal UVB (ultraviolet B) treatment conditions for vitamin D2 enhancement of freeze-dried ear mushroom, sample size (below 300 μm~whole), UV treatment temperature (30~60℃), treatment density (6.25~50.0 mg/cm2) and the samples mixing frequency (1~32 times) were treated differently. After that, chromaticity, vitamin D2 and ergosterol (vitamin D2 precursor) contents were investigated. As a result of the investigating, effective UVB treatment conditions for vitamin D2 enhancement are as follows. The sample sizes were 2~4 mm and finely crushed pieces. The treatment temperatures were 50℃ and 60℃. The treatment density was 12.5 to 25.0 mg/cm2, and the number of sample mixing was 8 times or more. As the amount of vitamin D2 increased by UVB treatment, the ergosterol content generally tended to decrease. However, under some UVB treatment conditions, the vitamin D2 content was not high despite the decrease of ergosterol content. Under the conditions set in this experiment, it was possible to obtain ear mushrooms with enhanced vitamin D2 up to 26,968.7 μg/100 g. Therefore, it is thought that the ear mushroom is highly likely to be used as a vitamin D source and nutritionally fortified food ingredient.