This study was conducted to know the optimal supplementary level of spent mushroom substrates (Flammulinavelutipes) as an energy source and fermentation period in manufacturing of rye silage. Whole crop rye was harvested at fullbloom stage and ensiled with spent mushroom substrates of 20%(S-20), 40%(S-40) and 60%(S-60) as fresh matter basis.Each silage was prepared in plastic buckets included with vinyl bag by three replications and fermented for 3, 6 and 9weeks, respectively. Moisture contents of whole crop rye at full bloom stage and spent mushroom substrates were 62.3%and 54.3%, respectively, and those of silages was ranged from 58% to 64%. Ether extracts content of silages wassignificantly (P<0.05) increased in 6 weeks of fermentation period. The pH of silages ranged from 4.46 to 5.05, andfluctuated in the changes by fermentation period beside of decreased with elapsing the period in the S-60. The organicacid content of silages was higher in the order of lactic acid, butyric acid, acetic acid and propionic acid. Lactic acidcontent was higher when fermented for 6 weeks compared to the other fermentation period. Flieg's score for estimation ofsilage quality ranged from 63 to 80, and was relatively high level in the S-20 and the S-40 fermented for 6 weeks, and washigh level in S-20, and was relatively low level in the silages fermented for 3 week. Hence, we suggest thatsupplementation of 20% spent mushroom substrates in fresh matter basis and fermentation for 6 weeks are resonable for agood quality of rye silage.