As part of our systematic study of Korean toxic mushrooms, we have investigated the constituents of Amanita subjunquillea. The column chromatographic separation of the MeOH extract of A. subjunquillea led to the isolation of four ergosterols, two cerebrosides and four cyclopeptides. Their structures were determined by spectroscopic methods to be (22E,24R)-$5{alpha},8{alpha}$-epidioxyergosta-6,9,22-triene-$3{eta}$-ol (1), (22E,24R)-$5{alpha},8{alpha}$-epidioxyergosta-6,22-dien-$3{eta}$-ol (2), (22E,24R)-$5{alpha},6{alpha}$-epoxyergosta-8,22-diene-$3{eta},7{eta}$-diol (3), (24S)-ergost-7-en-$3{eta}$-ol (4), 8,9-dihydrosoyacerebroside I (5), soyacerebroside I (6), $eta$-amanitin (7), phalloin (8), $alpha$-amanitin (9), and phalloidin (10). The compounds 1-6 and 8 were isolated for the first time from this mushroom. The isolated compounds were evaluated for the cytotoxicity against A549, SK-OV-3, SKMEL-2 and HCT15 cells. Compound 9 exhibited significant cytotoxic activity against A549, SKOV-3, SK-MEL-2 and HCT15 with $ED_{50}$ values of 1.47, 0.26, 1.57 and $1.32;{mu}M$, respectively.