Magnetic nanoparticle Fe3O4-immobilized guanidine (MNPs-Guanidine) as a novel magnetically interphase nanocatalyst was synthesized and characterized. MNPs-Guanidine catalyzed the synthesis of alpha-hydroxyphosphonates from aldehydes and dimethyl phosphite in solvent-free condition at 80 degrees C. The synthesis of alpha-acetoxyphosphonates through a one-pot reaction of aldehydes, dimethyl phosphite and acetic anhydride was also achieved using this catalyst in PEG at room temperature. The catalyst was recycled up to 10 times with little loss of activity. (C) 2013 Elsevier B.V. All rights reserved.