Residual biomasses from agro-industries in Paraguay, including soybean hulls (SBHs) and sugarcane bagasse (SCB), were studied as a source for nanocellulose extraction for the first time. For that purpose, both biomasses were delignified in a semi-pilot stainless-steel reactor, and the cellulose pulp was subjected to a bleaching process with NaClO (2.5%, w/v). The nanocellulose (CNC) was obtained after two-step acid hydrolysis. Firstly, the bleached cellulose was hydrolyzed with HCl (17%, w/w) for two hours at 60 °C to obtain microcrystals by removing most of the amorphous fraction. The celluloses were then treated with H2SO4 (65%, w/w) at 45 °C for 45 min to obtain nanocellulose. Physicochemical and morphological properties were analyzed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction analysis (XRD). The SBHs nanocellulose had a whisker-like form with a 230 ± 42 nm diameter and a 12 ± 2 nm height, and the SCB nanocellulose had a fibril-like form with a 103 ± 30 nm diameter and a height of 6 ± 3 nm. The nanocellulose from SBHs and SCB had good thermal stability as its degradation temperature started at 250 °C. Furthermore, the nanocellulose obtained was negatively charged and formed stable dispersion in water at 0.1 mg/mL concentration and a pH of around 6.5.