Example embodiments of the present invention relate to a method of forming a dielectric thin film and a method of fabricating a semiconductor memory device having the same. Other example embodiments of the present invention relate to a method of forming a ZrO.sub.2 thin film and a method of fabricating a capacitor of a semiconductor memory device using the ZrO.sub.2 thin film as a dielectric layer. A method of forming a ZrO.sub.2 thin film may include supplying a zirconium precursor on a substrate maintained at a desired temperature, thereby forming a chemisorption layer of the precursor on the substrate. The zirconium precursor may be a tris(N-ethyl-N-methylamino)(tert-butoxy) zirconium precursor. The substrate having the chemisorption layer of the precursor may be exposed to the plasma atmosphere of oxygen-containing gas for a desired time, thereby forming a Zr oxide layer on the substrate, and a method of fabricating a capacitor of a semiconductor memory device having the ZrO.sub.2 thin film.