From the leaves of Brassica juncea, three kaempferol glycosides, kaempferol-3-O-(2-O-sinapoyl)-$eta$-D-glucopyranosyl-($1{ ightarrow}2$)-$eta$-D-glucopyranoside-7-O-$eta$-D-glucopyranoside (1), kaempferol-3-O-$eta$-D-glucopyranosyl-($1{ ightarrow}2$)-$eta$-D-glucopyranoside-7-O-$eta$-D-glucopyranosyl-($1{ ightarrow}6$)-$eta$-D-glucopyranoside (2), and kaempferol-3-O-(2-O-sinapoyl)-$eta$-D-glucopyranosyl-($1{ ightarrow}2$)-$eta$-D-glucopyranoside-7-O-$eta$-D-glucopyranosyl-(1{ ightarrow}6)-$eta$-D-glucopyranoside (3) were isolated and the structures elucidated on the basis of spectral and chemical evidences. Antioxidant activities were determined by measuring the scavenging activities on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and peroxynitrite ($ONOO^-$). Compounds 1 and 3 showed good antioxidant activities with respective $IC_{50}$ values of 28.61 and $36.93;{mu}M$ toward DPPH; respective $IC_{50}$ values of 9.79 and $11.40;{mu}M$ toward $ONOO^-$. However, compound 2 showed no DPPH scavenging activity and weak $ONOO^-$ scavenging activity with an $IC_{50}$ value of $32.00;{mu}M$.