The content of vitamin $D_2$, including its precursor ergosterol, was determined in some cultivated mushrooms to manufacture fortified Doenjang (Korean traditional soybean paste) with vitamin D by supplementation with mushroom. Ergosterol was the most abundant sterol in the mushrooms (50 to 140 mg/100 g dry weight) but the ergocalciferol portion made up only 0.065% (Pleurotus eryngii) to 2.5% (stipe part of Lentinus edodes, shiitake) of the total vitamin $D_2$ of each mushroom. Changes in these compounds in L. edodes caused by UV or solar irradiation were also evaluated. Ergocalciferol content in the pileus part of L. edodes went up to $424;{mu}g/100;g$ dry weight and ergosterol levels reached 139.3 mg per 100 g dry weight at maximum levels. Ergocalciferol content increased about 50% when exposed to solar radiation and increased 377% with UV irradiation. These compounds level in Doenjang was enriched as much as supplied UV irradiated L. edodes powder to before fermentation, and the supplemented mushroom did not influence the palatability of Doenjang.