Water contamination caused by toxic cadmium metal ions is a worldwide problem. There is a need to explore new methods of cadmium removal from water. The green algae Enteromorpha flexuosa, obtained from the Red Sea in Yanbu, Saudi Arabia, was used to prepare iron nanoparticles. TEM, FT-IR, XRD, and SEM techniques were used to characterize the prepared nanoparticles. The prepared nanoparticle's surface was rough, with nanoparticle sizes ranging from 10 to 50 nm. The developed nanoparticles were used to adsorb cadmium ions from water in batch mode. With a 25.0 µg/L concentration, a temperature of 25˚C, 7.0 pH, 60 minutes contact time and 0.5 g/L dose, the maximum removal of cadmium was 48.2 µg/g. The sorption efficiency was measured using the Dubinin-Radushkevich, Temkin, Langmuir and Freundlich models. The amounts of ΔG° were -8.0, -9.93 and -12.24 kJ/mol while the values of ΔS° and ΔH° were -30.96 x 10-3 kJ/mol and 37.79 x 10-2 kJ/mol. These data confirmed the endothermic nature of cadmium metal ions removal. Along with the liquid film diffusion process, the adsorption adopted the kinetics of pseudo-second-order type. The recorded adsorption method is fast, cost-effective, and environmentally friendly and can be applied for testing the elimination of cadmium metal ions in natural waters.