A new alkaloid, identified as (E)-2-(4-hydroxyphenyl)-3-(pyridazin-3-yl)-acrylaldehyde, named oleradazine, was isolated from Portulaca oleracea L., and the structure was elucidated using spectroscopic methods, including 1D and 2D NMR spectroscopic and UHPLC-ESI-QTOF/MS methods. In addition, the compound was used to investigate its anti-inflammatory activity in lipopolysaccharide-stimulated macrophages. It was suggested that the oleradazine can significantly inhibit the inflammatory factors, interleukin 1β and nitric oxide in lipopolysaccharide-stimulated RAW 264.7 cells by enzyme-linked immunosorbent assays. © 2021 Informa UK Limited, trading as Taylor & Francis Group.