Seven new terpenoids, namely, guaiane (<b>1</b>-<b>4</b>), eudesmane (<b>5</b>), and bisabolane (<b>6</b>) sesquiterpenoids and a furanone (<b>7</b>), were isolated from the aerial parts of <i>Ammoides atlantica</i>, a herbaceous plant growing in Algeria, together with eight known compounds. All metabolites were characterized by their 1D and 2D NMR and HRESIMS data. A combined DFT/NMR method was applied to study the relative configurations of <b>1</b>-<b>4</b>, <b>6</b>, and <b>7</b>. All compounds, except <b>2</b>, were assayed against MCF-7, A375, A549, HaCaT, and Jurkat cell lines. Compounds <b>8</b>, <b>10</b>, and <b>11</b> induced a dose-dependent reduction in cell viability with different potency on almost all cell lines used. The most active compounds, <b>8</b> and <b>10</b>, were studied to assess their potential apoptotic effects and cell cycle inhibition.