| Summary: | In this study, we evaluated antioxidant, antihyperuricemic, and herbicidal activities of essential oils (EOs) from <i>Piper cubeba</i> Bojer and <i>Piper nigrum</i> L.; two pepper species widely distributed in tropics, and examined their chemical compositions. Dried berries of <i>P. cubeba</i> and <i>P. nigrum</i> were hydro-distilled to yield essential oil (EO) of 1.23 and 1.11% dry weight, respectively. In the antioxidant assay, the radical scavenging capacities of <i>P. cubeba</i> EO against DPPH and ABTS free radicals were 28.69 and 24.13% greater than <i>P. nigrum</i>, respectively. In the antihyperuricemic activity, <i>P. cubeba</i> EO also exhibited stronger inhibitory effects on xanthine oxidase (IC<sub>50</sub> = 54.87 µg/mL) than <i>P. nigrum</i> EO (IC<sub>50</sub> = 77.11 µg/mL). In the herbicidal activity, <i>P. cubeba</i> EO showed greater inhibition on germination and growth of <i>Bidens pilosa</i> and <i>Echinochloa crus-galli</i> than <i>P. nigrum</i> EO. Besides, <i>P. cubeba</i> EO decreased 15.98–73.00% of photosynthesis pigments of <i>B. pilosa</i> and <i>E. crus-galli</i>, while electrolyte leakages, lipid peroxidations, prolines, phenolics, and flavonoids contents were increased 10.82–80.82% at 1.93 mg/mL dose. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analyses revealed that <i>P. nigrum</i> and <i>P. cubeba</i> EOs principally possessed complex mixtures of monoterpenes and sesquiterpenes. Terpinen-4-ol (42.41%), α-copaene (20.04%), and γ-elemene (17.68%) were the major components of <i>P. cubeba</i> EO, whereas β-caryophyllene (51.12%) and β-thujene (20.58%) were the dominant components of <i>P. nigrum</i> EO. Findings of this study suggest both <i>P. cubeba</i> and <i>P. nigrum</i> EOs were potential to treat antioxidative stress and antihyperuricemic related diseases. In addition, the EOs of the two plants may be useful to control <i>B. pilosa</i> and <i>E. crus-galli</i>, the two invasive and problematic weeds in agriculture practice.
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