Previous work demonstrated that a commercial formulation of piperonyl butoxide (PBO) did inhibit the activity of some plant proteolytic enzymes. In this paper, the effect of pure PBO and nine pure PBO homologues (PBOH) appropriately synthesized toward bromelain and papain was studied in hydrocarbon solution using the bis(2-ethylhexyl)sodium sulfosuccinate (AOT) reverse micellar system. This study establishes that the majority of these compounds show, in vitro, interesting protease inhibition activities. The benzodioxole and dihydrobenzofuran structures, in particular, 5-[2-(2-butoxyethoxy)ethoxymethyl]-benzo[1,3]dioxole (EN 1-40) and 6-[2-(2-butoxyethoxy)ethoxymethyl]-5-propyl-2,3-dihydrobenzofuran (EN 16-5), respectively, appear to be responsible for protease inhibition. Measures of octanol/water partition coefficients on PBO and PBOH have demonstrated that water solubility plays a fundamental role in the expression of protease inhibition activity.