A new flavonoid glucoside derivative, patuletin 3 -O-(2- O-feruloyl)-β-d-glucuronopyranosyl-(1→2)-β-d-glucopyranoside, named atriplexin IV (1), and three new triterpenoid saponin derivatives, two sulfonylated, β-d-glucopyranosyl-3 -O-(2- O-sulfo-β-d-galactopyranosyl)-(1→2)-α-l-arabinopyranoside-30-alolean-12-en-28-oate (2), named atriplexogenin I, β-d-glucopyranosyl-3- O-(2- O-sulfo-β-d-galactopyranosyl)-(1→2)-α-l-arabinopyranoside)-30-hydroxyolean-12-en-28-oate (3), named atriplexogenin II, and β-d-glucopyranosyl-3 -O-(β-d-glucopyranosyl-(1→2)-β-d-galactopyranosyl-(1→2)-α-l-arabinopyranoside)-30-alolean-12-en-28-oate (4), named atriplexogenin III, were isolated by silica gel column and semipreparative HPLC chromatography from the n-butanol extract of the salt marsh plant Atriplex tatarica. In addition, two known secondary metabolites, patuletin3 -O-β-d-apiofuranosyl-(1‴→2″)-β-d-glucopyranoside (5) and patuletin 3 -O-5‴- O-feruloyl-β-d-apiofuranosyl-(1‴→2″)-β-d-glucopyranoside (6), were isolated for the first time from A. tatarica. The structures of the isolated compounds were elucidated by 1D and 2D NMR, HRESIMS, IR, and UV data. Antibacterial activity by the microdilution method and antibiofilm activity against P. aeruginosa were assessed. Compound 5 possesses significant antibacterial activity, while the most potent antibiofilm agent is compound 2.