<jats:p><jats:bold>BACKGROUND AND PURPOSE</jats:bold>Frankincense, the gum resin derived from<jats:italic>Boswellia</jats:italic>species, showed anti‐inflammatory efficacy in animal models and in pilot clinical studies. Boswellic acids (BAs) are assumed to be responsible for these effects but their anti‐inflammatory efficacy<jats:italic>in vivo</jats:italic>and their molecular modes of action are incompletely understood.<jats:p><jats:bold>EXPERIMENTAL APPROACH</jats:bold>A protein fishing approach using immobilized BA and surface plasmon resonance (SPR) spectroscopy were used to reveal microsomal prostaglandin E<jats:sub>2</jats:sub>synthase‐1 (mPGES1) as a BA‐interacting protein. Cell‐free and cell‐based assays were applied to confirm the functional interference of BAs with mPGES1. Carrageenan‐induced mouse paw oedema and rat pleurisy models were utilized to demonstrate the efficacy of defined BAs<jats:italic>in vivo</jats:italic>.<jats:p><jats:bold>KEY RESULTS</jats:bold>Human mPGES1 from A549 cells or<jats:italic>in vitro</jats:italic>‐translated human enzyme selectively bound to BA affinity matrices and SPR spectroscopy confirmed these interactions. BAs reversibly suppressed the transformation of prostaglandin (PG)H<jats:sub>2</jats:sub>to PGE<jats:sub>2</jats:sub>mediated by mPGES1 (IC<jats:sub>50</jats:sub> = 3–10 µM). Also, in intact A549 cells, BAs selectively inhibited PGE<jats:sub>2</jats:sub>generation and, in human whole blood, β‐BA reduced lipopolysaccharide‐induced PGE<jats:sub>2</jats:sub>biosynthesis without affecting formation of the COX‐derived metabolites 6‐keto PGF<jats:sub>1α</jats:sub>and thromboxane B<jats:sub>2</jats:sub>. Intraperitoneal or oral administration of β‐BA (1 mg·kg<jats:sup>−1</jats:sup>) suppressed rat pleurisy, accompanied by impaired levels of PGE<jats:sub>2</jats:sub>and β‐BA (1 mg·kg<jats:sup>−1</jats:sup>, given i.p.) also reduced mouse paw oedema, both induced by carrageenan.<jats:p><jats:bold>CONCLUSIONS AND IMPLICATIONS</jats:bold>Suppression of PGE<jats:sub>2</jats:sub>formation by BAs via interference with mPGES1 contribute to the anti‐inflammatory effectiveness of BAs and of frankincense, and may constitute a biochemical basis for their anti‐inflammatory properties.