Edible insects are a potential and sustainable protein resource. Various extraction methods are used to process edible insects. However, the residue fraction is discarded after protein extraction because of its poor functional properties, despite having a high protein content. This study was conducted to improve the functional properties of re-extracted protein from the raw and hydrolysed protein extraction residues, and to demonstrate the most effective condition of extraction buffer. Residues from Hermetia illucens L. protein water extraction and enzymatic hydrolysis extraction were hydrated using different pH buffers (0.1 M HCl, distilled water, and 0.1 M NaOH). Compared to the pH of the extract from the re-dissolved residue, the proteins from hydrolysed samples were acidic. Changes in colour values were observed for the different buffers and hydrolysis conditions applied. Protein solubility, foaming properties, and emulsifying properties of the protein improved after hydrolysis. In conclusion, hydrolysed protein extraction using the swelling method under alkaline conditions may improve the protein functionality of the residue fraction in H. illucens.