In Algerian Centaurea riaeana has been used in folk medicine for the treatment of several inflammatory disorders. Our investigation aimed to investigate the antioxidant, anti-inflamatory and cytoxicity effect of n-BuOH extract of Centaurea riaeana Rchb.f (BECR). The results showed that BECR extract which was safe up to a dose level of 2000 mg/kg, had high levels of polyphenols and flavonoids BECR extract exhibited a good antoxidant activity in a concentration dependent manner in different models , DPPH° (IC50=19.39±2.37 µg/mL), ABTS (IC50=12.67±1.16 μg/mL), reducing power (A0.50 = 94.33±0.24 μg/mL), CUPRAC (A0.50 = 10.89±0.43 μg/mL), and galvinoxyl radical (GOR) (IC50:11.99±1.06 μg/mL). Furthermore, BECR develops anti-rheumatoid arthritic effect, as mentioned by inhibition of protein denaturation assay (IC50=167.75±8.66 µg/mL) and stabilization of HRBC membrane anti-membrane lysis (HRBC assay) (IC50=114.95±8.04 µg/mL). BECR successfully reduced the swelling in both the early and the late (of carrageenan-evoked oedema. Notably, our findings demonstrated that higher concentrations of the plant extract had a significant effect on reducing cell viability in both HT29 and OV2008 cell lines. The effectiveness of BECR in combating ROS ,inflammation, and combating both HT29 and OV2008 cancer cell lines might be influenced by the synergistic action of its polyphenol constituents indicated for the first time in this plant by by liquid chromatography tandem mass spectrometry analysis.(LC-MS/M)S).