A novel alkaloid identified as methyl 8,9-dihydroxy-11-oxo-6,11-dihydro-5H-benzo[d]pyrrolo[1,2-a]azepine-3-carboxylate, named portulacatone A (1) with six known compounds Oleracein E (2), 6,7-dihdroxy-3,4-dihydro-2H-isoquinolin-1-one (3), N-trans-p-coumaroytyramine (4), 9H-carbazole (5), isoaspergin (6) and flavoglaucin (7) were obtained from Portulaca oleracea L., while compounds (5–7) were isolated from the plant for the first time. The new structure was identified by using UHPLC-ESI-Q-TOF/MS, 1D, 2D NMR and the others were proved by 1H-NMR and 13C NMR that comparing with previous reports. It was suggested that the portulacatone A (1) can significantly inhibit the inflammatory factor, interleukin-1β (IL-1β) in the RAW 264.7 cells induced by LPS. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.