Classical swine fever virus (CSFV) is an OIE-listed disease in need of more effective diagnostic tools for its control and detection.  In particular, the availability of diagnostically sensitive and specific DIVA vaccine-compatible tests would increase the chance of successful control of the disease.  The aim of this study was to develop a CSFV Erns IgG AlphaLISA® for serum and oral fluids that would complement currently available CSFV E2 DIVA vaccines.  After assay development, its performance was evaluated using a panel of well-characterized serum (n = 760) and individual (n = 528) or pen-based (n = 30) oral fluid samples from 4 groups of animals: (1) unvaccinated and uninoculated; (2) unvaccinated and inoculated with wild-type CSFV (ALD strain); (3) uninoculated and vaccinated with a live CSFV (LOM strain) vaccine; and (4) uninoculated and vaccinated with live CSFV marker vaccine.  Overall, the CSFV Erns IgG AlphaLISA® showed diagnostic sensitivity and specificity of 97.9% and 99.8% for serum and 99.7% and 100% for oral fluids, respectively.  Thus, the assay combined DIVA capability with rapid turnaround and simplicity of use.