Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 21 2 2026 07 12 195 204 Norsyafiqah Ahmad Safri Department of Biomedical Science, Faculty of Medicine, Universiti Malaya, 50603, Kuala Lumpur, Malaysia Fei Wen Cheong Department of Parasitology, Faculty of Medicine, Universiti Malaya, 50603, Kuala Lumpur, Malaysia Nur Zulaikha Zulkefli Department of Parasitology, Faculty of Medicine, Universiti Malaya, 50603, Kuala Lumpur, Malaysia Abolghasem Siyadatpanah Department of Microbiology, Faculty of Medicine, Infectious Diseases Research Center, Gonabad University of Medical Sciences, Gonabad, Iran Roghayeh Norouzi Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran Yee Ling Lau Department of Parasitology, Faculty of Medicine, Universiti Malaya, 50603, Kuala Lumpur, Malaysia 2025 07 07 2026 07 12 Background: Malaria remains a major global health burden, with increasing challenges posed by drug-resistant Plasmodium species. Another emerging threat is Plasmodium knowlesi, a zoonotic parasite responsible for rising human infections in Southeast Asia, particularly Malaysia. This study investigates the in vitro antimalarial activity of Silybum marianum (milk thistle) and Trigonella foenum-graecum (fenugreek) seed extracts against P. knowlesi, and their cytotoxicity against mammalian cells. Methods: Using schizont maturation inhibition assay, P. knowlesi cultures were exposed to serial dilutions of both plant hydroethanolic extracts (0.20–100.00 μg/mL). Chloroquine was used as positive control. Cytotoxicity was evaluated on Vero cells using the MTT assay. Results: Both extracts exhibited moderate antimalarial activity, with IC₅₀ values of 16.12 ± 1.02 μg/mL (S. marianum) and 17.08 ± 1.26 μg/mL (T. foenum-graecum). Cytotoxicity testing showed that the extracts were non-toxic to mammalian cells, with CC₅₀ values of 84.76 ± 15.12 μg/mL (S. marianum) and 72.75 ± 15.81 μg/mL (T. foenum-graecum). The selectivity indices were 5.26 and 4.26, respectively, indicating moderate selectivity towards the parasite over mammalian cells. Conclusion: Both S. marianum and T. foenum-graecum demonstrate promising antimalarial potential against P. knowlesi in vitro, with acceptable cytotoxicity profiles. These findings support further investigation into their bioactive constituents and mechanism of action, offering preliminary evidence for their potential development as alternative antimalarial agents targeting zoonotic malaria. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/4659 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/4659/1494