The (100) surface of MgAl 2 O 4 is evaluated as a substrate for the thin film deposition of the relaxor ferroelectric PbMg 1/3 Nb 2/3 O 3 (65%)–PbTiO 3 (35%). With a lattice mismatch of less than 0.5%, this film-substrate combination presents a geometrical template for growth that is far superior to that formed with other commercially available oxide substrates. Films were deposited using the pulsed laser deposition technique and were characterized in terms of their crystallographic, microstructural, and dielectric properties. From a crystallographic perspective the films show excellent cube-on-cube epitaxy, are highly oriented, and show no evidence of the frequently observed parasitic pyrochlore phase. With the exception of a few faceted surface structures, the film’s microstructure is single-crystal-like, exhibiting a sharp film-substrate interface, a smooth top surface, and no discernable granularity. The dielectric response shows the frequency-dependent diffuse phase transition characteristic of a relaxor material, but with less frequency dispersion and a smaller maximum in the dielectric constant. Taken together, the results suggest that the (100) MgAl 2 O 4 substrate could prove to be an effective substrate material, not only for the PbMg 1/3 Nb 2/3 O 3 (65%)–PbTiO 3 (35%) system, but also for a number of other important lattice-matched ferroelectric, relaxor, and ferroelectric superlattice systems.