Abstract The species Waltheria viscosissima A.St.–Hil, Malvaceae, which is known as ‘malva-branca', is traditionally used in the Brazilian northeast for the treatment of coughs. This research looks towards reporting the isolation of phytoconstituents of W. viscosissima, as well as the quantification of its phenolics, total flavonoid content, and free radical scavenging potential, along with an evaluation of its larvicidal activity against Aedes aegypti larvae. Chromatographic techniques were used to isolate the compounds and a structural elucidation was performed by 1D and 2D NMR. The quantification of total phenolics and flavonoids and the DPPH˙ radical scavenging activity was determined through spectrophotometric methods. Consequently, the phytochemical investigation led to the identification of fourteen compounds from the aerial parts of the W. viscosissima: steroids, triterpenes, alkaloids, and eight flavonoids previously reported in the literature. The quantification of compounds showed that the aerial parts extract possessed high concentration of flavonoids, while the roots extract were rich in other phenolic compounds. At the DPPH˙ free radical scavenging assay, the roots extract presented EC50 = 77.32 ± 4.37 µg/ml and the aerial parts extracts showed EC50 = 118.10 ± 1.21 µg/ml. W. viscosissima roots extract showed the most potent larvicidal activity against Ae. aegypti (LC50 = 4.78 mg/ml), with the potential of being used in effective and economically viable preparations that can be catered for domestic use towards controlling the vector insect of severe diseases, such as dengue and Zika.