Objective: To identify the residue determinants of the serospecificity and sero-cross-reactivity of dengue virus (DENV) envelope protein domain 3 (ED3), which contains two major putative epitopes of DENV. Methods: We constructed ED3 from DENV3 (3ED3) and DENV4 (4ED3), and six epitope-grafted variants, where we transferred epitope 1 (L304I, K305D, V309M, and S310A) and/or epitope 2 (D383N, K384S, K387T, and N389H) of 4ED3 onto 3ED3 and vice-versa. Swiss albino mice aged 3-4 weeks were immunized against wildtype and epitope-grafted ED3 variants and anti-ED3 IgG antibody responses were determined using ELISA. Results: Mouse immunization using 3ED3 and 4ED3 generated serotype-specific antisera, as expected. Similarly, most epitopegrafted ED3s produced antisera serospecific to the template ED3 with little or no cross-recognition of ED3 of the serotype from which the epitopes were taken. These indicated that a mere grafting of the epitope was not sufficient to transfer serospecificity, contrary to our expectations. However, one epitope-grafted ED3 mutant, where epitope 1 of 3ED3 was grafted onto 4ED3 (4ED3epi1), generated antisera that was serospecific to both 4ED3 and 3ED3. Conclusions: The 4ED3epi1 is a chimeric ED3 that produces antisera possessing serospecificity to both 3ED3 and 4ED3 onto a common 4ED3 scaffold. The 4ED3epi1, therefore, provides a unique tool for analyzing serospecificity and sero-cross-reactivity in dengue. We believe that chimeric ED3 may provide a template for future recombinant ED3 possessing serospecificity of multiple DENVs onto a single scaffold and may pave a way developing tri-and/or tetravalent anti-DENV antisera.