A series of tetranuclear lanthanide (Ln = Tb, Dy, Ho) hydroxo clusters has been synthesized by reaction of LnCl(3)center dot 6H(2)O (Ln = Tb (1), Dy (2), Ho (3)) with o-vanilin based schiff base ligand 2-(2,3 dihydroxpropyl imino methyl) 6-methoxy phenol (H3L) in methanol and in the presence of triethylamine as base. The solid state structures of all the products were established by single crystal X-ray diffraction technique. Magnetism studies reveal that Dy-4 analogue exhibits slow magnetic relaxation at low temperatures.