Chronic periodontitis is a destructive inflammatory disease that involves alveolar bone resorption and can cause tooth loss. More significantly this chronic inflammatory disease is now known to be associated with comorbidities including rheumatoid arthritis, low infant birth weights and atherosclerosis. The disease is associated with dysbiosis of the dental plaque biofilm, with Porphyromonas gingivalis considered a keystone pathogen. P. gingivalis produces many virulence factors of which the cysteine proteases the Arg-gingipains (RgpA, RgpB) and Lys-gingipain (Kgp) are considered most important. Inhibitors of these proteases have been devised; however none are ideal, being non-specific or toxic or both. The gingipain nascent polypeptides are produced with N-terminal propeptides that render them inactive until they are cleaved at the cell surface. We recently demonstrated recombinant proteins mimicking the RgpB and Kgp propeptides (rRgpB-PP and rKgp-PP respectively) were able to inhibit purified RgpB and Kgp respectively whilst not inhibiting host proteases and also reduce whole bacterial cell proteolytic activity. The RgpA and RgpB catalytic domains are 97% identical yet the propeptides share only 78% identity. In this study we tested a recombinant RgpA propeptide (rRgpA-PP) demonstrating inhibition in the nanomolar range against Arg-gingipain activities in P. gingivalis strains that have been collected from around the world. We also show using RgpA and RgpB mutants that rRgpA-PP inhibits whole cell RgpA and RgpB equally well, but notably it inhibits both RgpA and RgpB 5-fold more effectively than the rRgpB-PP. Therefore, rRgpA-PP shows promise as specific inhibitor therapeutic to reduce Arg-gingipain activity of P. gingivalis in the periodontal pockets of patients with chronic periodontitis.