The present study was carried out to determine the antibacterial activities from the isolated phytochemicals of Piper retrofractum and Piper arborescens. Fractionation and purification of the extract of P. retrofractum yielded piperine (1), methyl piperate (2) and N-isobutyl-2E,4E,14Z-eicosatrienamide (3), while extracts of P. arborescens yielded sesartemin (4), diayangambin (5), and 3-(3,4-dimethoxybenzyl)-4-(3',4',5'-trimethoxybenzyl)- tetrahydrofuran-2-ol (6). The structures of the isolated phytochemicals were established by analysis of their spectroscopic data, as well as the comparison with that of reported data. The antibacterial activity of the isolated phytochemicals was also evaluated by using the micro-dilution method. Compound (1) was found to show the significant activity against Staphylococcus aureus and Bacillus subtilis with MIC values of 225 µg/mL. This study reports amides and lignans as compounds that could be involved in antibacterial activity of Piper retrofractum and Piper arborescens. However, more detailed experiments are needed to explore the underlying antibacterial mechanism further.