Eight compounds, including one sphingolipid (1), two flavonoids (2, 3), four sterols (4–7), and one amino acid (8), had been isolated and purified from Amaranthus retroflexus L. Their structures were elucidated on the basis of spectroscopic analyses, including 1D and 2D NMR and ESI-MS. Among them, 1-O-β-D-glucopyranosyl-(2S,3R,4R,8E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-1,3,4-octadecanetriol-8-ene (1) was identified as a new compound, and α-spinasteryl-3-O-β-D-glucopyranoside (4), 3β,12β,20(S)-trihydroxydammar-24-ene-6-O-β-D-glucopyranoside (6), and 2β,3β-dihydroxy-30-norolean-12,20(29)-diene-23,28-dioic acid 28-O-β-D-glucopyranosyl ester (7) were isolated from this plant for the first time. This is the first more comprehensive report on chemical compositions of Amaranthus retroflexus L.