Nanocomposite superabsorbent were prepared with nano sodium alginate used as the backbone, acrylic acid (AA) and acrylamide (Aam) as monomer, N, N-methylenebisacrylamide (MBA) as crosslinker, potassium persulfate (KPS) as initiator and montmorillonite as filler. The properties of superabsorbent nanocomposites were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Based on the FTIR spectra of the superabsorbent nanocomposite with in situ polymerization which have urea content, ammonium and potassium, can be seen from FTIR peaks to be compared with pure fertilizer. The highest swelling capacity obtained in urea nanocomposite SA 5 has a swelling capacity of 580 g/g, this is due to the presence of hydrophilic groups in the superabsorbent and urea, so it causes a high swelling capasity. Furthermore, ammonium nanocomposite has high enough swelling capacity of 465 g/g, while potassium nanocomposite is 420 g/g, respectively. The results of the study are good enough for the application of agricultural fertilizers.