Dengue fever causes significant numbers of victims in Indonesia every year. As of the 17th week of 2024, dengue fever has claimed the lives of 621 people out of a total of 88,593 cases across the country. This is due to environmental conditions that are suitable for the life cycle of Aedes aegypti. Efforts to eradicate Aedes aegypti larvae have been made, one of which involves using a larvicide called temephos or abate. However, abate leaves a lasting residue. This research aimed to identify natural alternatives to abate. Previous studies have explored the use of seaweed to control mosquitoes, but none have investigated Caulerpa serrulata (Forsskål) J.Agardh, 1837, despite its abundance in Indonesian waters and its rapid spread along the coast, much like a pest. This study analyzed the larvicidal activity of Caulerpa serrulata in both extract form and as titanium dioxide nanoparticles (TiO2-NPs), as well as their environmental safety. The LC50 values for the extract and TiO2-NPs against Aedes aegypti larvae were 0.16 ppm and 0.14ppm, respectively. The particle size of the extract ranged from 13.012 to 275.177µm, with 94.599% of the particles in the nanoparticle size range. Meanwhile, the particle size of TiO2-NPs ranged from 0.012 to 2000µm, with 96.402% in the nanoparticle size range. Further observations on the environmental safety of TiO2-NPs revealed that they are not only safe for fish but also enhance their resistance to fungi. However, the TiO2-NPs tend to settle at the bottom of the water. Therefore, further research is needed to develop methods for producing uniformly sized TiO2-NPs from Caulerpa serrulata and to assess their impact on non-vector organisms that live at the bottom of the water and in the soil substrate.