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ABSTRACTCurcuma longa(C. longa) rhizome extract has been traditionally used to treat many infections. Curcumin, a pure compound isolated from the plant, has been documented to possess a wide spectrum of pharmacological effects. The present study aimed to investigate the effects of Thai medicinal plant extracts including C. longaextract and Curcumin on Acanthamoeba triangularis, a causative agent of human Acanthamoebakeratitis. The parasite was isolated from the recreational reservoir at Walailak University, Thailand. The organism was identified as A. triangularisusing morphology and 18S rDNA nucleotide sequences. The pathogen was tested for their susceptibility to ethanol extracts of Thai medicinal plants based on eye infection treatment. The ethanol C. longaextract showed the strongest anti-Acanthamoebaactivity against both the trophozoites and cysts, followed by Coscinium fenestratum, Coccinia grandis, and Acmella oleraceaextracts, respectively. After 24 h, 95% reduction of trophozoite viability was significantly decreased following the treatment with C. longaextract at 125 µg/mL, compared with the control (P < 0.05). The extract at 1,000 µg/mL inhibited 90% viability of Acanthamoebacyst within 24 h, compared with the control. It was found that the cysts treated with C. longaextract at 500 µg/mL demonstrated abnormal shape after 24 h. The MIC values of C. longaextract and Curcumin against the trophozoites were 125 and 62.5 µg/mL, respectively. While the MICs of the extract and curcumin against the cysts were 500 and 1,000 µg/mL, respectively. The results suggested the potential medicinal benefits of C. longaextract and Curcumin as the alternative treatment of Acanthamoebainfections.