Clove essential oils (CEOs) are widely studied because of their biological potential; however, their applications are limited because of their water immiscibility. Microemulsions (MEs) can protect, deliver, and enhance the biological activities of CEOs, including their antioxidant and cytotoxic activities. In this research, the effects of ethanol as a cosurfactant and the polysorbate 80:cosurfactant mixture (S_mix = 1:0, 9:1, 7:1, 5:1, 3:1, and 1:1) on the formation of CEO-MEs were evaluated via a pseudo-ternary phase diagram. After 35 days, all the systems produced clear, monodisperse, and thermodynamically stable MEs, characterized by average sizes below 25.6 nm and low polydispersity index values (<0.21). The S_mix dose–response experiments without CEO revealed that the S_mix ratios of 1:1 and 3:1 resulted in the lowest cytotoxicity to HT-29 (colorectal adenocarcinoma) cells. The antioxidant capacity of the CEO-ME was greater than that of the CEO. Finally, the CEO-MEs enhanced the in vitro cytotoxic activity of the CEO against Caco-2, HT-29, HeLa, PC-3, and A549 cancer cells. These findings provide valuable information for the development of low-energy clove essential oil MEs for potential incorporation into functional foods and pharmaceutical products.