<p>Hydrothermal liquefaction (HTL) offers a sustainable method for producing bio-oil from algal biomass. Evaluating the microwave- and ultrasonic-pretreatment HTL and examining the quality of bio-oil obtained from HTL of marine macroalgae, namely <i>Sargassum</i> and <i>Caulerpa</i>, are the main objectives and novelty behind this work. Algal feedstocks were pretreated by microwave (500 W and 600 W) or ultrasonic (50 W and 75 W) before heating up to 350 oC for 35 min in the HTL reactor. Results showed that <i>Sargassum</i> and <i>Caulerpa</i> displayed completely different behaviors in pretreatment. The bio-oil yield from <i>Sargassum</i> went up by increasing microwave and ultrasonic pretreatment power. Although the microwave-assisted HTL of <i>Caulerpa</i> yielded more bio-oil than ultrasonication, it did not achieve the bio-oil production levels of the conventional HTL process. The highest yield and HHV of bio-oil were obtained for 22.4 wt% and 35.56 MJ/kg for <i>Sargassum</i> with microwave pretreatment, while the pretreatment power had a negative effect on those from <i>Caulerpa</i> by decreasing quantity and quality. It was also found that 56.41% of the bio-oil components were acids for <i>Caulerpa</i>, and 34.6% were ketones for <i>Sargassum</i> under conventional HTL. Thermal weight loss analysis showed that 70.4% of the bio-oil derived from <i>Sargassum</i> obtained by HTL following ultrasonic pretreatment possesses a boiling point below 243 °C which suggests the higher quality of the bio-oil derived from <i>Sargassum</i> with a significant proportion of lighter compounds. The results indicate that the bio-oil obtained from <i>Sargassum</i> had a higher quantity and quality than that for <i>Caulerpa</i>. Besides, the carbon recovery of bio-oil indicated the highest amount of carbon (70.12 wt%) was achieved through the microwave pretreatment of <i>Sargassum</i>. Also, differences in the cellular structure of the raw materials resulted in different quality and quantity of bio-oil.</p>