Toxoplasma gondii is a zoonotic protozoa of economic significance in livestock. Infected livestock meat and products act as a source of T. gondii infection in humans. Current drugs against T. gondii are limited by hypersensitivity and toxicity, and are not effective against the encysted bradyzoite stage of T. gondii. Thus, there is urgent need for safe and effective therapeutic agents against T. gondii. Marine algae possess potent antifungal and antibacterial properties, but there are no reports on its anti-protozoal activity. Therefore, in this study we obtained nhexane and methanol extracts of green algae (Chlorophyceae) and analyzed their content by high performance liquid chromatography coupled with mass spectrometry, as well as tested their in vitro anti-Toxoplasma activities. Compared to the n-hexane extract of Chlorophyceae, the methanol extract contained higher content of flavonoids/ polyphenols, alkaloids (elaeocarpidine and auramine), and artemisic acid. Importantly, the methanol extract had more potent anti-Toxoplasma activity (IC50=4.43 ± 1.26 μg/mL) than the n-hexane extract (IC50=23.32 ± 3.97 μg/ mL), corroborating the higher content of flavonoids, alkaloids, and artemisic acid in methanol extracts than in nhexane extract. The anti-Toxoplasma IC50 values of the methanol and n-hexane extracts were 34-fold and 7-fold lower than their respective cytotoxic IC50 values in human fibroblast cell line. Consistent with our findings, flavonoids, alkaloids and artemisic acid have previously been shown to have potent anti-Toxoplasma activity. Together, our results show that Chlorophyceae contains significant amounts of bioactive compounds with potent anti-Toxoplasma activity.