DC magnetic susceptibilities χ were measured for Ni(OH) 2 monolayer nanoclusters (Ni-MNC) which were randomly comprised by amorphous SiO 2 . The χ showed the Curie-Weiss behavior between about 100 and 300K, and it deviated from the Curie-Weiss law below about 100K. The χ-data were compared with the high temperature series expansion (HTSE) theory for 2D Ising ferromagnet, and it was found that the short range order effect in the 2D Ising system was dominant for the magnetism of Ni-MNC between 16 and 100K. The analysis by the superparamagnetic model showed a gradual increase of the ferromagnetic Ni 2 + cluster size in each Ni-MNC. The quantum size effect in Ni-MNC was also discussed by the modified HTSE theory.