Kaempferia parviflora Wall.ex.Baker is a Thai medicinal herb that has high antioxidant and anti-inflammatoryactivities. Apoptotic effects of the herbal extract alone and in combination with chemotherapeutic drugs, paclitaxeland camptothecin, were here studied in the human promonocytic leukemic U937 cell line. K. parviflora extractsuppressed cell proliferation and decreased cell viability in a dose- and time-dependent manner as assessedusing the trypan blue exclusion assay. Staining of extract-treated cells with propidium iodide and examinationunder a fluorescence microscope showed condensed nuclei and apoptotic bodies. Mitochondrial transmembranepotential (MTP) decreased after treatment and the number of cells with decreased MTP also increased.Furthermore, activation of caspase-3 was found in herbal extract-treated cells. When the extract was combinedwith paclitaxel, an additive effect on U937 cell apoptosis was obtained, whereas camptothecin exerted anantagonistic effect.